less命令

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命令用途

less 是一个功能强大的 Linux/Unix 文件查看工具，支持分页显示和交互式浏览文件内容，特别适合查看大文件或实时日志。

常用用法示例

1. 基本文件查看

   less access.log

   打开 access.log 文件，支持上下翻页、搜索等交互操作，按 q 退出。

2. 显示行号

   less -N config.conf
         1  [server]
         2  port=8080
         3  host=localhost

   每行内容前显示行号，方便定位。

3. 实时监控日志更新

   less +F debug.log

   进入实时监控模式（类似 tail -f），按 Ctrl+C 停止监控，回到普通浏览模式。

4. 从指定行开始查看

   less +20 error.log

   直接跳转到 error.log 的第 20 行开始显示。

5. 搜索关键词

   less system.log

   输入 /error 后回车，高亮显示所有 “error” 关键词，按 n 跳转到下一个匹配项。

6. 查看压缩文件

   less file.gz

   自动解压并查看 gzip 压缩文件内容（需系统支持）。

7. 跳转到文件末尾

   less +G app.log

   直接显示文件最后一行，适合快速查看日志结尾。

8. 忽略大小写搜索

   less -i data.txt

   输入 /WARNING 会匹配 “warning”、”Warning” 等大小写变体。

常用参数选项

• -N, –LINE-NUMBERS
  显示行号，方便内容定位。
• -i, –ignore-case
  搜索时忽略大小写（需先输入此参数）。
• -F, –quit-if-one-screen
  若文件内容可一屏显示，则直接输出并退出（类似 cat）。
• -S, –chop-long-lines
  截断超长行而不是自动换行，保持页面整洁。
• -M, –LONG-PROMPT
  显示更详细的提示信息（包括文件位置百分比）。
• -R, –RAW-CONTROL-CHARS
  正确显示 ANSI 颜色转义字符（如彩色日志）。
• -g, –HILITE-SEARCH
  仅高亮最后一次匹配的搜索关键词。
• -X, –no-init
  退出后保留内容在屏幕（不执行清屏操作）。

原厂文档

NAME

       less - display the contents of a file in a terminal

SYNOPSIS

       less -?
       less --help
       less -V
       less --version
       less [-[+]aABcCdeEfFgGiIJKLmMnNqQrRsSuUVwWX~]
            [-b space] [-h lines] [-j line] [-k keyfile]
            [-{oO} logfile] [-p pattern] [-P prompt] [-t tag]
            [-T tagsfile] [-x tab,...] [-y lines] [-[z] lines]
            [-# shift] [+[+]cmd] [--] [filename]...
       (See the OPTIONS section for alternate option syntax with long
       option names.)

DESCRIPTION

       Less is a program similar to more(1), but it has many more
       features.  Less does not have to read the entire input file before
       starting, so with large input files it starts up faster than text
       editors like vi(1).  Less uses termcap (or terminfo on some
       systems), so it can run on a variety of terminals.  There is even
       limited support for hardcopy terminals.  (On a hardcopy terminal,
       lines which should be printed at the top of the screen are
       prefixed with a caret.)

       Commands are based on both more and vi.  Commands may be preceded
       by a decimal number, called N in the descriptions below.  The
       number is used by some commands, as indicated.

COMMANDS

       In the following descriptions, ^X means control-X.  ESC stands for
       the ESCAPE key; for example ESC-v means the two character sequence
       "ESCAPE", then "v".

       h or H Help: display a summary of these commands.  If you forget
              all the other commands, remember this one.

       SPACE or ^V or f or ^F
              Scroll forward N lines, default one window (see option -z
              below).  If N is more than the screen size, only the final
              screenful is displayed.  Warning: some systems use ^V as a
              special literalization character.

       z      Like SPACE, but if N is specified, it becomes the new
              window size.

       ESC-SPACE
              Like SPACE, but scrolls a full screenful, even if it
              reaches end-of-file in the process.

       ENTER or RETURN or ^N or e or ^E or j or ^J
              Scroll forward N lines, default 1.  The entire N lines are
              displayed, even if N is more than the screen size.

       d or ^D
              Scroll forward N lines, default one half of the screen
              size.  If N is specified, it becomes the new default for
              subsequent d and u commands.

       b or ^B or ESC-v
              Scroll backward N lines, default one window (see option -z
              below).  If N is more than the screen size, only the final
              screenful is displayed.

       w      Like ESC-v, but if N is specified, it becomes the new
              window size.

       y or ^Y or ^P or k or ^K
              Scroll backward N lines, default 1.  The entire N lines are
              displayed, even if N is more than the screen size.
              Warning: some systems use ^Y as a special job control
              character.

       u or ^U
              Scroll backward N lines, default one half of the screen
              size.  If N is specified, it becomes the new default for
              subsequent d and u commands.

       J      Like j, but continues to scroll beyond the end of the file.

       K or Y Like k, but continues to scroll beyond the beginning of the
              file.

       ESC-) or RIGHTARROW
              Scroll horizontally right N characters, default half the
              screen width (see the -# option).  If a number N is
              specified, it becomes the default for future RIGHTARROW and
              LEFTARROW commands.  While the text is scrolled, it acts as
              though the -S option (chop lines) were in effect.

       ESC-( or LEFTARROW
              Scroll horizontally left N characters, default half the
              screen width (see the -# option).  If a number N is
              specified, it becomes the default for future RIGHTARROW and
              LEFTARROW commands.

       ESC-} or ^RIGHTARROW
              Scroll horizontally right to show the end of the longest
              displayed line.

       ESC-{ or ^LEFTARROW
              Scroll horizontally left back to the first column.

       r or ^R or ^L
              Repaint the screen.

       R      Repaint the screen, discarding any buffered input.  That
              is, reload the current file.  Useful if the file is
              changing while it is being viewed.

       F      Scroll forward, and keep trying to read when the end of
              file is reached.  Normally this command would be used when
              already at the end of the file.  It is a way to monitor the
              tail of a file which is growing while it is being viewed.
              (The behavior is similar to the "tail -f" command.)  To
              stop waiting for more data, enter the interrupt character
              (usually ^C).  On systems which support poll(2) you can
              also use ^X or the character specified by the --intr
              option.  If the input is a pipe and the --exit-follow-on-
              close option is in effect, less will automatically stop
              waiting for data when the input side of the pipe is closed.

       ESC-F  Like F, but as soon as a line is found which matches the
              last search pattern, the terminal bell is rung and forward
              scrolling stops.

       g or < or ESC-<
              Go to line N in the file, default 1 (beginning of file).
              (Warning: this may be slow if N is large.)

       G or > or ESC->
              Go to line N in the file, default the end of the file.
              (Warning: this may be slow if N is large, or if N is not
              specified and standard input, rather than a file, is being
              read.)

       ESC-G  Same as G, except if no number N is specified and the input
              is standard input, goes to the last line which is currently
              buffered.

       p or % Go to a position N percent into the file.  N should be
              between 0 and 100, and may contain a decimal point.

       P      Go to the line containing byte offset N in the file.

       {      If a left curly bracket appears in the top line displayed
              on the screen, the { command will go to the matching right
              curly bracket.  The matching right curly bracket is
              positioned on the bottom line of the screen.  If there is
              more than one left curly bracket on the top line, a number
              N may be used to specify the N-th bracket on the line.

       }      If a right curly bracket appears in the bottom line
              displayed on the screen, the } command will go to the
              matching left curly bracket.  The matching left curly
              bracket is positioned on the top line of the screen.  If
              there is more than one right curly bracket on the bottom
              line, a number N may be used to specify the N-th bracket on
              the line.

       (      Like {, but applies to parentheses rather than curly
              brackets.

       )      Like }, but applies to parentheses rather than curly
              brackets.

       [      Like {, but applies to square brackets rather than curly
              brackets.

       ]      Like }, but applies to square brackets rather than curly
              brackets.

       ESC-^F Followed by two characters, acts like {, but uses the two
              characters as open and close brackets, respectively.  For
              example, "ESC ^F < >" could be used to go forward to the >
              which matches the < in the top displayed line.

       ESC-^B Followed by two characters, acts like }, but uses the two
              characters as open and close brackets, respectively.  For
              example, "ESC ^B < >" could be used to go backward to the <
              which matches the > in the bottom displayed line.

       m      Followed by any lowercase or uppercase letter, marks the
              first displayed line with that letter.  If the status
              column is enabled via the -J option, the status column
              shows the marked line.

       M      Acts like m, except the last displayed line is marked
              rather than the first displayed line.

       '      (Single quote.)  Followed by any lowercase or uppercase
              letter, returns to the position which was previously marked
              with that letter.  Followed by another single quote,
              returns to the position at which the last "large" movement
              command was executed.  Followed by a ^ or $, jumps to the
              beginning or end of the file respectively.  Marks are
              preserved when a new file is examined, so the ' command can
              be used to switch between input files.

       ^X^X   Same as single quote.

       ESC-m  Followed by any lowercase or uppercase letter, clears the
              mark identified by that letter.

       /pattern
              Search forward in the file for the N-th line containing the
              pattern.  N defaults to 1.  The pattern is a regular
              expression, as recognized by the regular expression library
              supplied by your system.  By default, searching is case-
              sensitive (uppercase and lowercase are considered
              different); the -i option can be used to change this.  The
              search starts at the first line displayed (but see the -a
              and -j options, which change this).

              Certain characters are special if entered at the beginning
              of the pattern; they modify the type of search rather than
              become part of the pattern:

              ^N or !
                     Search for lines which do NOT match the pattern.

              ^E or *
                     Search multiple files.  That is, if the search
                     reaches the END of the current file without finding
                     a match, the search continues in the next file in
                     the command line list.

              ^F or @
                     Begin the search at the first line of the FIRST file
                     in the command line list, regardless of what is
                     currently displayed on the screen or the settings of
                     the -a or -j options.

              ^K     Highlight any text which matches the pattern on the
                     current screen, but don't move to the first match
                     (KEEP current position).

              ^R     Don't interpret regular expression metacharacters;
                     that is, do a simple textual comparison.

              ^S     Followed by a digit N between 1 and 5.  Only text
                     which has a non-empty match for the N-th
                     parenthesized SUB-PATTERN will be considered to
                     match the pattern.  (Supported only if less is built
                     with one of the regular expression libraries posix,
                     pcre, or pcre2.)  Multiple ^S modifiers can be
                     specified, to match more than one sub-pattern.

              ^W     WRAP around the current file.  That is, if the
                     search reaches the end of the current file without
                     finding a match, the search continues from the first
                     line of the current file up to the line where it
                     started.  If the ^W modifier is set, the ^E modifier
                     is ignored.

              ^L     The next character is taken literally; that is, it
                     becomes part of the pattern even if it is one of the
                     above search modifier characters.

       ?pattern
              Search backward in the file for the N-th line containing
              the pattern.  The search starts at the last line displayed
              (but see the -a and -j options, which change this).

              Certain characters are special as in the / command:

              ^N or !
                     Search for lines which do NOT match the pattern.

              ^E or *
                     Search multiple files.  That is, if the search
                     reaches the beginning of the current file without
                     finding a match, the search continues in the
                     previous file in the command line list.

              ^F or @
                     Begin the search at the last line of the last file
                     in the command line list, regardless of what is
                     currently displayed on the screen or the settings of
                     the -a or -j options.

              ^K     As in forward searches.

              ^R     As in forward searches.

              ^S     As in forward searches.

              ^W     WRAP around the current file.  That is, if the
                     search reaches the beginning of the current file
                     without finding a match, the search continues from
                     the last line of the current file up to the line
                     where it started.

       ESC-/pattern
              Same as "/*".

       ESC-?pattern
              Same as "?*".

       n      Repeat previous search, for N-th line containing the last
              pattern.  If the previous search was modified by ^N, the
              search is made for the N-th line NOT containing the
              pattern.  If the previous search was modified by ^E, the
              search continues in the next (or previous) file if not
              satisfied in the current file.  If the previous search was
              modified by ^R, the search is done without using regular
              expressions.  There is no effect if the previous search was
              modified by ^F or ^K.

       N      Repeat previous search, but in the reverse direction.

       ESC-n  Repeat previous search, but crossing file boundaries.  The
              effect is as if the previous search were modified by *.

       ESC-N  Repeat previous search, but in the reverse direction and
              crossing file boundaries.

       ESC-u  Undo search highlighting.  Turn off highlighting of strings
              matching the current search pattern.  If highlighting is
              already off because of a previous ESC-u command, turn
              highlighting back on.  Any search command will also turn
              highlighting back on.  (Highlighting can also be disabled
              by toggling the -G option; in that case search commands do
              not turn highlighting back on.)

       ESC-U  Like ESC-u but also clears the saved search pattern.  If
              the status column is enabled via the -J option, this clears
              all search matches marked in the status column.

       &pattern
              Display only lines which match the pattern; lines which do
              not match the pattern are not displayed.  If pattern is
              empty (if you type & immediately followed by ENTER), any
              filtering is turned off, and all lines are displayed.
              While filtering is in effect, an ampersand is displayed at
              the beginning of the prompt, as a reminder that some lines
              in the file may be hidden.  Multiple & commands may be
              entered, in which case only lines which match all of the
              patterns will be displayed.

              Certain characters are special as in the / command:

              ^N or !
                     Display only lines which do NOT match the pattern.

              ^R     Don't interpret regular expression metacharacters;
                     that is, do a simple textual comparison.

       :e [filename]
              Examine a new file.  If the filename is missing, the
              "current" file (see the :n and :p commands below) from the
              list of files in the command line is re-examined.  A
              percent sign (%) in the filename is replaced by the name of
              the current file.  A pound sign (#) is replaced by the name
              of the previously examined file.  However, two consecutive
              percent signs are simply replaced with a single percent
              sign.  This allows you to enter a filename that contains a
              percent sign in the name.  Similarly, two consecutive pound
              signs are replaced with a single pound sign.  The filename
              is inserted into the command line list of files so that it
              can be seen by subsequent :n and :p commands.  If the
              filename consists of several files, they are all inserted
              into the list of files and the first one is examined.  If
              the filename contains one or more spaces, the entire
              filename should be enclosed in double quotes (also see the
              -" option).

       ^X^V or E
              Same as :e.  Warning: some systems use ^V as a special
              literalization character.  On such systems, you may not be
              able to use ^V.

       :n     Examine the next file (from the list of files given in the
              command line).  If a number N is specified, the N-th next
              file is examined.

       :p     Examine the previous file in the command line list.  If a
              number N is specified, the N-th previous file is examined.

       :x     Examine the first file in the command line list.  If a
              number N is specified, the N-th file in the list is
              examined.

       :d     Remove the current file from the list of files.

       t      Go to the next tag, if there were more than one matches for
              the current tag.  See the -t option for more details about
              tags.

       T      Go to the previous tag, if there were more than one matches
              for the current tag.

       ^O^N or ^On
              Search forward in the file for the N-th next OSC 8
              hyperlink.

       ^O^P or ^Op
              Search backward in the file for the N-th previous OSC 8
              hyperlink.

       ^O^L or ^Ol
              Jump to the currently selected OSC 8 hyperlink.

       = or ^G or :f
              Prints some information about the file being viewed,
              including its name and the line number and byte offset of
              the bottom line being displayed.  If possible, it also
              prints the length of the file, the number of lines in the
              file and the percent of the file above the last displayed
              line.

       -      Followed by one of the command line option letters (see
              OPTIONS below), this will change the setting of that option
              and print a message describing the new setting.  If a ^P
              (CONTROL-P) is entered immediately after the dash, the
              setting of the option is changed but no message is printed.
              If the option letter has a numeric value (such as -b or
              -h), or a string value (such as -P or -t), a new value may
              be entered after the option letter.  If no new value is
              entered, a message describing the current setting is
              printed and nothing is changed.

       --     Like the - command, but takes a long option name (see
              OPTIONS below) rather than a single option letter.  You
              must press ENTER or RETURN after typing the option name.  A
              ^P immediately after the second dash suppresses printing of
              a message describing the new setting, as in the - command.

       -+     Followed by one of the command line option letters this
              will reset the option to its default setting and print a
              message describing the new setting.  (The "-+X" command
              does the same thing as "-+X" on the command line.)  This
              does not work for string-valued options.

       --+    Like the -+ command, but takes a long option name rather
              than a single option letter.

       -!     Followed by one of the command line option letters, this
              will reset the option to the "opposite" of its default
              setting and print a message describing the new setting.
              This does not work for numeric or string-valued options.

       --!    Like the -! command, but takes a long option name rather
              than a single option letter.

       _      (Underscore.)  Followed by one of the command line option
              letters, this will print a message describing the current
              setting of that option.  The setting of the option is not
              changed.

       __     (Double underscore.)  Like the _ (underscore) command, but
              takes a long option name rather than a single option
              letter.  You must press ENTER or RETURN after typing the
              option name.

       +cmd   Causes the specified cmd to be executed each time a new
              file is examined.  For example, +G causes less to initially
              display each file starting at the end rather than the
              beginning.

       V      Prints the version number of less being run.

       q or Q or :q or :Q or ZZ
              Exits less.

       The following seven commands may or may not be valid, depending on
       your particular installation.

       v      Invokes an editor to edit the current file being viewed.
              The editor is taken from the environment variable VISUAL if
              defined, or EDITOR if VISUAL is not defined, or defaults to
              "vi" if neither VISUAL nor EDITOR is defined.  See also the
              discussion of LESSEDIT under the section on PROMPTS below.

       ! shell-command
              Invokes a shell to run the shell-command given.  A percent
              sign (%) in the command is replaced by the name of the
              current file.  A pound sign (#) is replaced by the name of
              the previously examined file.  "!!" repeats the last shell
              command.  "!" with no shell command simply invokes a shell.
              If a ^P (CONTROL-P) is entered immediately after the !, no
              "done" message is printed after the shell command is
              executed.  On Unix systems, the shell is taken from the
              environment variable SHELL, or defaults to "sh".  On MS-
              DOS, Windows, and OS/2 systems, the shell is the normal
              command processor.

       # shell-command
              Similar to the "!" command, except that the command is
              expanded in the same way as prompt strings.  For example,
              the name of the current file would be given as "%f".

       | <m> shell-command
              <m> represents any mark letter.  Pipes a section of the
              input file to the given shell command.  The section of the
              file to be piped is between the position marked by the
              letter and the current screen.  The entire current screen
              is included, regardless of whether the marked position is
              before or after the current screen.  <m> may also be ^ or $
              to indicate beginning or end of file respectively.  If <m>
              is . or newline, the current screen is piped.  If a ^P
              (CONTROL-P) is entered immediately after the mark letter,
              no "done" message is printed after the shell command is
              executed.

       s filename
              Save the input to a file.  This works only if the input is
              a pipe, not an ordinary file.

       ^O^O
              Run a shell command to open the URI in the current OSC 8
              hyperlink, selected by a previous ^O^N or ^O^P command.  To
              find the shell command, the environment variable named
              "LESS_OSC8_xxx" is read, where "xxx" is the scheme from the
              URI (the part before the first colon), or is empty if there
              is no colon in the URI.  The value of the environment
              variable is then expanded in the same way as prompt strings
              (in particular, any instance of "%o" is replaced with the
              URI) to produce an OSC 8 "handler" shell command.  The
              standard output from the handler is an "opener" shell
              command which is then executed to open the URI.

              There are two special cases:

                     1.     If the URI begins with "#", the remainder of
                            the URI is taken to be the value of the id
                            parameter in another OSC 8 link in the same
                            file, and ^O^O will simply jump to that link.

                     2.     If the opener begins with the characters ":e"
                            followed by whitespace and a filename, then
                            instead of running the opener as a shell
                            command, the specified filename is opened in
                            the current instance of less.

              In a simple case where the opener accepts the complete URI
              as a command line parameter, the handler may be as simple
              as

              echo mybrowser '%o'

              In other cases, the URI may need to be modified, so the
              handler may have to do some manipulation of the %o value.

              If the LESS_OSC8_xxx variable is not set, the variable
              LESS_OSC8_ANY is tried.  If neither LESS_OSC8_xxx nor
              LESS_OSC8_ANY is set, links using the "xxx" scheme cannot
              be opened.  However, there are default handlers for the
              schemes "man" (used when LESS_OSC8_man is not set) and
              "file" (used when LESS_OSC8_file is not set), which should
              work on systems which provide the sed(1) command and a
              shell with syntax compatible with the Bourne shell sh(1).
              If you use LESS_OSC8_ANY to override LESS_OSC8_file, you
              must set LESS_OSC8_file to "-" to indicate that the default
              value should not be used, and likewise for LESS_OSC8_man.

              The URI passed to an OSC8 handler via %o is guaranteed not
              to contain any single quote or double quote characters, but
              it may contain any other shell metacharacters such as
              semicolons, dollar signs, ampersands, etc.  The handler
              should take care to appropriately quote parameters in the
              opener command, to prevent execution of unintended shell
              commands in the case of opening a URI which contains shell
              metacharacters.  Also, since the handler command is
              expanded like a command prompt, any metacharacters
              interpreted by prompt expansion (such as percent, dot,
              colon, backslash, etc.) must be escaped with a backslash
              (see the PROMPTS section for details).

       ^X     When the "Waiting for data" message is displayed, such as
              while in the F command, pressing ^X will stop less from
              waiting and return to a prompt.  This may cause less to
              think that the file ends at the current position, so it may
              be necessary to use the R or F command to see more data.
              The --intr option can be used to specify a different
              character to use instead of ^X.  This command works only on
              systems that support the poll(2) function.  On systems
              without poll(2), the interrupt character (usually ^C) can
              be used instead.

OPTIONS

       Command line options are described below.  Most options may be
       changed while less is running, via the "-" command.

       Some options may be given in one of two forms: either a dash
       followed by a single letter, or two dashes followed by a long
       option name.  A long option name may be abbreviated as long as the
       abbreviation is unambiguous.  For example, --quit-at-eof may be
       abbreviated --quit, but not --qui, since both --quit-at-eof and
       --quiet begin with --qui.  Some long option names are in
       uppercase, such as --QUIT-AT-EOF, as distinct from --quit-at-eof.
       Such option names need only have their first letter capitalized;
       the remainder of the name may be in either case.  For example,
       --Quit-at-eof is equivalent to --QUIT-AT-EOF.

       Options are also taken from the environment variable "LESS".  For
       example, to avoid typing "less -options ..." each time less is
       invoked, you might tell csh:

       setenv LESS "-options"

       or if you use sh:

       LESS="-options"; export LESS

       On MS-DOS and Windows, you don't need the quotes, but you should
       be careful that any percent signs in the options string are not
       interpreted as an environment variable expansion.

       The environment variable is parsed before the command line, so
       command line options override the LESS environment variable.  If
       an option appears in the LESS variable, it can be reset to its
       default value on the command line by beginning the command line
       option with "-+".

       Some options like -k or -D require a string to follow the option
       letter.  The string for that option is considered to end when a
       dollar sign ($) is found.  For example, you can set two -D options
       like this:

       LESS="Dnwb$Dsbw"

       If the --use-backslash option appears earlier in the options, then
       a dollar sign or backslash may be included literally in an option
       string by preceding it with a backslash.  If the --use-backslash
       option is not in effect, then backslashes are not treated
       specially, and there is no way to include a dollar sign in the
       option string.

       -? or --help
              This option displays a summary of the commands accepted by
              less (the same as the h command).  (Depending on how your
              shell interprets the question mark, it may be necessary to
              quote the question mark, thus: "-\?".)

       -a or --search-skip-screen
              By default, forward searches start at the top of the
              displayed screen and backwards searches start at the bottom
              of the displayed screen (except for repeated searches
              invoked by the n or N commands, which start after or before
              the "target" line respectively; see the -j option for more
              about the target line).  The -a option causes forward
              searches to instead start at the bottom of the screen and
              backward searches to start at the top of the screen, thus
              skipping all lines displayed on the screen.

       -A or --SEARCH-SKIP-SCREEN
              Causes all forward searches (not just non-repeated
              searches) to start just after the target line, and all
              backward searches to start just before the target line.
              Thus, forward searches will skip part of the displayed
              screen (from the first line up to and including the target
              line).  Similarly backwards searches will skip the
              displayed screen from the last line up to and including the
              target line.  This was the default behavior in less
              versions prior to 441.

       -bn or --buffers=n
              Specifies the amount of buffer space less will use for each
              file, in units of kilobytes (1024 bytes).  By default 64 KB
              of buffer space is used for each file (unless the file is a
              pipe; see the -B option).  The -b option specifies instead
              that n kilobytes of buffer space should be used for each
              file.  If n is -1, buffer space is unlimited; that is, the
              entire file can be read into memory.

       -B or --auto-buffers
              By default, when data is read from a pipe, buffers are
              allocated automatically as needed.  If a large amount of
              data is read from the pipe, this can cause a large amount
              of memory to be allocated.  The -B option disables this
              automatic allocation of buffers for pipes, so that only
              64 KB (or the amount of space specified by the -b option)
              is used for the pipe.  Warning: use of -B can result in
              erroneous display, since only the most recently viewed part
              of the piped data is kept in memory; any earlier data is
              lost.  Lost characters are displayed as question marks.

       -c or --clear-screen
              Causes full screen repaints to be painted from the top line
              down.  By default, full screen repaints are done by
              scrolling from the bottom of the screen.

       -C or --CLEAR-SCREEN
              Same as -c, for compatibility with older versions of less.

       -d or --dumb
              The -d option suppresses the error message normally
              displayed if the terminal is dumb; that is, lacks some
              important capability, such as the ability to clear the
              screen or scroll backward.  The -d option does not
              otherwise change the behavior of less on a dumb terminal.

       -Dxcolor or --color=xcolor
              Changes the color of different parts of the displayed text.
              x is a single character which selects the type of text
              whose color is being set:

              B      Binary characters.

              C      Control characters.

              E      Errors and informational messages.

              H      Header lines and columns, set via the --header
                     option.

              M      Mark letters in the status column.

              N      Line numbers enabled via the -N option.

              P      Prompts.

              R      The rscroll character.

              S      Search results.

              W      The highlight enabled via the -w option.

              1-5    The text in a search result which matches the first
                     through fifth parenthesized sub-pattern.  Sub-
                     pattern coloring works only if less is built with
                     one of the regular expression libraries posix, pcre,
                     or pcre2.

              d      Bold text.

              k      Blinking text.

              s      Standout text.

              u      Underlined text.

              The uppercase letters and digits can be used only when the
              --use-color option is enabled.  When text color is
              specified by both an uppercase letter and a lowercase
              letter, the uppercase letter takes precedence.  For
              example, error messages are normally displayed as standout
              text.  So if both "s" and "E" are given a color, the "E"
              color applies to error messages, and the "s" color applies
              to other standout text.  The lowercase letters refer to
              bold and underline text formed by overstriking with
              backspaces (see the -U option) and to non-content text
              (such as line numbers and prompts), but not to text
              formatted using ANSI escape sequences with the -R option
              (but see the note below for different behavior on Windows
              and MS-DOS).

              A lowercase letter may be followed by a + to indicate that
              the normal format change and the specified color should
              both be used.  For example, -Dug displays underlined text
              as green without underlining; the green color has replaced
              the usual underline formatting.  But -Du+g displays
              underlined text as both green and in underlined format.

              color is either a 4-bit color string or an 8-bit color
              string:

              A 4-bit color string is one or two characters, where the
              first character specifies the foreground color and the
              second specifies the background color as follows:

              b      Blue

              c      Cyan

              g      Green

              k      Black

              m      Magenta

              r      Red

              w      White

              y      Yellow

              The corresponding uppercase letter denotes a brighter shade
              of the color.  For example, -DNGk displays line numbers as
              bright green text on a black background, and -DEbR displays
              error messages as blue text on a bright red background.  If
              either character is a "-" or is omitted, the corresponding
              color is set to that of normal text.

              An 8-bit color string is one or two decimal integers
              separated by a dot, where the first integer specifies the
              foreground color and the second specifies the background
              color.  Each integer is a value between 0 and 255 inclusive
              which selects a "CSI 38;5" color value (see
              https://en.wikipedia.org/wiki/ANSI_escape_code#SGR).  If
              either integer is a "-" or is omitted, the corresponding
              color is set to that of normal text.

              A 4-bit or 8-bit color string may be followed by one or
              more of the following characters to set text attributes in
              addition to the color.

              s or ~ Standout (reverse video)

              u or _ Underline

              d or * Bold

              l or & Blinking

              On MS-DOS and Windows, the --color option behaves differ‐
              ently from what is described above in these ways:

              •      The bold (d and *) and blinking (l and &) text at‐
                     tributes at the end of a color string are not sup‐
                     ported.

              •      Lowercase color selector letters refer to text for‐
                     matted by ANSI escape sequences with -R, in addition
                     to overstruck and non-content text (but see -Da).

              •      For historical reasons, when a lowercase color se‐
                     lector letter is followed by a numeric color value,
                     the number is not interpreted as an "CSI 38;5" color
                     value as described above, but instead as a 4-bit
                     CHAR_INFO.Attributes value, between 0 and 15 inclu‐
                     sive (see
                     https://learn.microsoft.com/en-us/windows/console/char-info-str).

                     To avoid confusion, it is recommended that the
                     equivalent letters rather than numbers be used after
                     a lowercase color selector on MS-DOS/Windows.

              •      Numeric color values ("CSI 38;5" color) following an
                     uppercase color selector letter are not supported on
                     systems earlier than Windows 10.

              •      Only a limited set of ANSI escape sequences to set
                     color in the content work correctly.  4-bit color
                     sequences work, but "CSI 38;5" color sequences do
                     not.

              •      The -Da option makes the behavior of --color more
                     similar to its behavior on non-MS-DOS/Windows sys‐
                     tems by (1) making lowercase color selector letters
                     not affect text formatted with ANSI escape se‐
                     quences, and (2) allowing "CSI 38;5" color sequences
                     in the content work by passing them to the terminal
                     (only on Windows 10 and later; on earlier Windows
                     systems, such sequences do not work regardless of
                     the setting of -Da).

       -e or --quit-at-eof
              Causes less to automatically exit the second time it reach‐
              es end-of-file.  By default, the only way to exit less is
              via the "q" command.

       -E or --QUIT-AT-EOF
              Causes less to automatically exit the first time it reaches
              end-of-file.

       -f or --force
              Forces non-regular files to be opened.  (A non-regular file
              is a directory or a device special file.)  Also suppresses
              the warning message when a binary file is opened.  By de‐
              fault, less will refuse to open non-regular files.  Note
              that some operating systems will not allow directories to
              be read, even if -f is set.

       -F or --quit-if-one-screen
              Causes less to automatically exit if the entire file can be
              displayed on the first screen.

       -g or --hilite-search
              Normally, less will highlight ALL strings which match the
              last search command.  The -g option changes this behavior
              to highlight only the particular string which was found by
              the last search command.  This can cause less to run some‐
              what faster than the default.

       -G or --HILITE-SEARCH
              The -G option suppresses all highlighting of strings found
              by search commands.

       -hn or --max-back-scroll=n
              Specifies a maximum number of lines to scroll backward.  If
              it is necessary to scroll backward more than n lines, the
              screen is repainted in a forward direction instead.  (If
              the terminal does not have the ability to scroll backward,
              -h0 is implied.)

       -i or --ignore-case
              Causes searches to ignore case; that is, uppercase and low‐
              ercase are considered identical.  This option is ignored if
              any uppercase letters appear in the search pattern; in oth‐
              er words, if a pattern contains uppercase letters, then
              that search does not ignore case.

       -I or --IGNORE-CASE
              Like -i, but searches ignore case even if the pattern con‐
              tains uppercase letters.

       -jn or --jump-target=n
              Specifies a line on the screen where the "target" line is
              to be positioned.  The target line is the line specified by
              any command to search for a pattern, jump to a line number,
              jump to a file percentage or jump to a tag.  The screen
              line may be specified by a number: the top line on the
              screen is 1, the next is 2, and so on.  The number may be
              negative to specify a line relative to the bottom of the
              screen: the bottom line on the screen is -1, the second to
              the bottom is -2, and so on.  Alternately, the screen line
              may be specified as a fraction of the height of the screen,
              starting with a decimal point: .5 is in the middle of the
              screen, .3 is three tenths down from the first line, and so
              on.  If the line is specified as a fraction, the actual
              line number is recalculated if the terminal window is re‐
              sized.  If the --header option is used and the target line
              specified by -j would be obscured by the header, the target
              line is moved to the first line after the header.  While
              the --header option is active, the -S option is ignored,
              and lines longer than the screen width are truncated.

              If any form of the -j option is used, repeated forward
              searches (invoked with "n" or "N") begin at the line imme‐
              diately after the target line, and repeated backward
              searches begin at the target line, unless changed by -a or
              -A.  For example, if "-j4" is used, the target line is the
              fourth line on the screen, so forward searches begin at the
              fifth line on the screen.  However nonrepeated searches
              (invoked with "/" or "?")  always begin at the start or end
              of the current screen respectively.

       -J or --status-column
              Displays a status column at the left edge of the screen.
              The character displayed in the status column may be one of:

              >      The line is chopped with the -S option, and the text
                     that is chopped off beyond the right edge of the
                     screen contains a match for the current search.

              <      The line is horizontally shifted, and the text that
                     is shifted beyond the left side of the screen con‐
                     tains a match for the current search.

              =      The line is both chopped and shifted, and there are
                     matches beyond both sides of the screen.

              *      There are matches in the visible part of the line
                     but none to the right or left of it.

              a-z, A-Z
                     The line has been marked with the corresponding let‐
                     ter via the m command.

       -kfilename or --lesskey-file=filename
              Causes less to open and interpret the named file as a
              lesskey(1) binary file.  Multiple -k options may be speci‐
              fied.  If the LESSKEY or LESSKEY_SYSTEM environment vari‐
              able is set, or if a lesskey file is found in a standard
              place (see KEY BINDINGS), it is also used as a lesskey
              file.  Note the warning under "--lesskey-content" below.

       --lesskey-src=filename
              Causes less to open and interpret the named file as a
              lesskey(1) source file.  If the LESSKEYIN or LESSKEYIN_SYS‐
              TEM environment variable is set, or if a lesskey source
              file is found in a standard place (see KEY BINDINGS), it is
              also used as a lesskey source file.  Prior to version 582,
              the lesskey program needed to be run to convert a lesskey
              source file to a lesskey binary file for less to use.  New‐
              er versions of less read the lesskey source file directly
              and ignore the binary file if the source file exists.  Note
              the warning under "--lesskey-content" below.

       --lesskey-content=text
              Causes less to interpret the specified text as the contents
              of a lesskey(1) source file.  In the text, lesskey lines
              may be separated by either newlines as usual, or by semi‐
              colons.  A literal semicolon may be represented by a back‐
              slash followed by a semicolon.

              Warning: certain environment variables such as LESS,
              LESSSECURE, LESSCHARSET and others, which are used early in
              startup, cannot be set in a file specified by a command
              line option (--lesskey, --lesskey-src or --lesskey-con‐
              tent).  When using a lesskey file to set environment vari‐
              ables, it is safer to use the default lesskey file, or to
              specify the file using the LESSKEYIN or LESSKEY_CONTENT en‐
              vironment variables rather than using a command line op‐
              tion.

       -K or --quit-on-intr
              Causes less to exit immediately (with status 2) when an in‐
              terrupt character (usually ^C) is typed.  Normally, an in‐
              terrupt character causes less to stop whatever it is doing
              and return to its command prompt.  Note that use of this
              option makes it impossible to return to the command prompt
              from the "F" command.

       -L or --no-lessopen
              Ignore the LESSOPEN environment variable (see the INPUT
              PREPROCESSOR section below).  This option can be set from
              within less, but it will apply only to files opened subse‐
              quently, not to the file which is currently open.

       -m or --long-prompt
              Causes less to prompt verbosely (like more(1)), with the
              percent into the file.  By default, less prompts with a
              colon.

       -M or --LONG-PROMPT
              Causes less to prompt even more verbosely than more(1).

       -n or --line-numbers
              Suppresses line numbers.  The default (to use line numbers)
              may cause less to run more slowly in some cases, especially
              with a very large input file.  Suppressing line numbers
              with the -n option will avoid this problem.  Using line
              numbers means: the line number will be displayed in the
              verbose prompt and in the = command, and the v command will
              pass the current line number to the editor (see also the
              discussion of LESSEDIT in PROMPTS below).

       -N or --LINE-NUMBERS
              Causes a line number to be displayed at the beginning of
              each line in the display.

       -ofilename or --log-file=filename
              Causes less to copy its input to the named file as it is
              being viewed.  This applies only when the input file is a
              pipe, not an ordinary file.  If the file already exists,
              less will ask for confirmation before overwriting it.

       -Ofilename or --LOG-FILE=filename
              The -O option is like -o, but it will overwrite an existing
              file without asking for confirmation.

              If no log file has been specified, the -o and -O options
              can be used from within less to specify a log file.  With‐
              out a file name, they will simply report the name of the
              log file.  The "s" command is equivalent to specifying -o
              from within less.

       -ppattern or --pattern=pattern
              The -p option on the command line is equivalent to specify‐
              ing +/pattern; that is, it tells less to start at the first
              occurrence of pattern in the file.

       -Pprompt or --prompt=prompt
              Provides a way to tailor the three prompt styles to your
              own preference.  This option would normally be put in the
              LESS environment variable, rather than being typed in with
              each less command.  Such an option must either be the last
              option in the LESS variable, or be terminated by a dollar
              sign.
               -Ps followed by a string changes the default (short)
              prompt to that string.
               -Pm changes the medium (-m) prompt.
               -PM changes the long (-M) prompt.
               -Ph changes the prompt for the help screen.
               -P= changes the message printed by the = command.
               -Pw changes the message printed while waiting for data (in
              the "F" command).

              All prompt strings consist of a sequence of letters and
              special escape sequences.  See the section on PROMPTS for
              more details.

       -q or --quiet or --silent
              Causes moderately "quiet" operation: the terminal bell is
              not rung if an attempt is made to scroll past the end of
              the file or before the beginning of the file.  If the ter‐
              minal has a "visual bell", it is used instead.  The bell
              will be rung on certain other errors, such as typing an in‐
              valid character.  The default is to ring the terminal bell
              in all such cases.

       -Q or --QUIET or --SILENT
              Causes totally "quiet" operation: the terminal bell is nev‐
              er rung.  If the terminal has a "visual bell", it is used
              in all cases where the terminal bell would have been rung.

       -r or --raw-control-chars
              Causes "raw" control characters to be displayed.  The de‐
              fault is to display control characters using the caret no‐
              tation; for example, a control-A (octal 001) is displayed
              as "^A" (with some exceptions as described under the -U op‐
              tion).  Warning: when the -r option is used, less cannot
              keep track of the actual appearance of the screen (since
              this depends on how the screen responds to each type of
              control character).  Thus, various display problems may re‐
              sult, such as long lines being split in the wrong place.

              USE OF THE -r OPTION IS NOT RECOMMENDED.

       -R or --RAW-CONTROL-CHARS
              Like -r, but only ANSI "color" escape sequences and OSC 8
              hyperlink sequences are output in "raw" form.  Unlike -r,
              the screen appearance is maintained correctly, provided
              that there are no escape sequences in the file other than
              these types of escape sequences.  Color escape sequences
              are only supported when the color is changed within one
              line, not across lines.  In other words, the beginning of
              each line is assumed to be normal (non-colored), regardless
              of any escape sequences in previous lines.  For the purpose
              of keeping track of screen appearance, these escape se‐
              quences are assumed to not move the cursor.

              OSC 8 hyperlinks are sequences of the form:

                   ESC ] 8 ; ... \7

              The terminating sequence may be either a BEL character (\7)
              or the two-character sequence "ESC \".

              ANSI color escape sequences are sequences of the form:

                   ESC [ ... m

              where the "..." is zero or more color specification charac‐
              ters.  You can make less think that characters other than
              "m" can end ANSI color escape sequences by setting the en‐
              vironment variable LESSANSIENDCHARS to the list of charac‐
              ters which can end a color escape sequence.  And you can
              make less think that characters other than the standard
              ones may appear between the ESC and the m by setting the
              environment variable LESSANSIMIDCHARS to the list of char‐
              acters which can appear.

       -s or --squeeze-blank-lines
              Causes consecutive blank lines to be squeezed into a single
              blank line.  This is useful when viewing nroff output.

       -S or --chop-long-lines
              Causes lines longer than the screen width to be chopped
              (truncated) rather than wrapped.  That is, the portion of a
              long line that does not fit in the screen width is not dis‐
              played until you press RIGHT-ARROW.  The default is to wrap
              long lines; that is, display the remainder on the next
              line.  See also the --wordwrap option.

       -ttag or --tag=tag
              The -t option, followed immediately by a TAG, will edit the
              file containing that tag.  For this to work, tag informa‐
              tion must be available; for example, there may be a file in
              the current directory called "tags", which was previously
              built by ctags(1) or an equivalent command.  If the envi‐
              ronment variable LESSGLOBALTAGS is set, it is taken to be
              the name of a command compatible with global(1), and that
              command is executed to find the tag.  (See
              http://www.gnu.org/software/global/global.html).  The -t
              option may also be specified from within less (using the -
              command) as a way of examining a new file.  The command
              ":t" is equivalent to specifying -t from within less.

       -Ttagsfile or --tag-file=tagsfile
              Specifies a tags file to be used instead of "tags".

       -u or --underline-special
              Causes backspaces and carriage returns to be treated as
              printable characters; that is, they are sent to the termi‐
              nal when they appear in the input.

       -U or --UNDERLINE-SPECIAL
              Causes backspaces, tabs, carriage returns and "formatting
              characters" (as defined by Unicode) to be treated as con‐
              trol characters; that is, they are handled as specified by
              the -r option.

              By default, if neither -u nor -U is given, backspaces which
              appear adjacent to an underscore character are treated spe‐
              cially: the underlined text is displayed using the termi‐
              nal's hardware underlining capability.  Also, backspaces
              which appear between two identical characters are treated
              specially: the overstruck text is printed using the termi‐
              nal's hardware boldface capability.  Other backspaces are
              deleted, along with the preceding character.  Carriage re‐
              turns immediately followed by a newline are deleted.  Other
              carriage returns are handled as specified by the -r option.
              Unicode formatting characters, such as the Byte Order Mark,
              are sent to the terminal.  Text which is overstruck or un‐
              derlined can be searched for if neither -u nor -U is in ef‐
              fect.

              See also the --proc-backspace, --proc-tab, and --proc-re‐
              turn options.

       -V or --version
              Displays the version number of less.

       -w or --hilite-unread
              Temporarily highlights the first "new" line after a forward
              movement of a full page.  The first "new" line is the line
              immediately following the line previously at the bottom of
              the screen.  Also highlights the target line after a g or p
              command.  The highlight is removed at the next command
              which causes movement.  If the --status-line option is in
              effect, the entire line (the width of the screen) is high‐
              lighted.  Otherwise, only the text in the line is high‐
              lighted, unless the -J option is in effect, in which case
              only the status column is highlighted.

       -W or --HILITE-UNREAD
              Like -w, but temporarily highlights the first new line af‐
              ter any forward movement command larger than one line.

       -xn,... or --tabs=n,...
              Sets tab stops.  If only one n is specified, tab stops are
              set at multiples of n.  If multiple values separated by
              commas are specified, tab stops are set at those positions,
              and then continue with the same spacing as the last two.
              For example, "-x9,17" will set tabs at positions 9, 17, 25,
              33, etc.  The default for n is 8.

       -X or --no-init
              Disables sending the termcap initialization and deinitial‐
              ization strings to the terminal.  This is sometimes desir‐
              able if the deinitialization string does something unneces‐
              sary, like clearing the screen.

       -yn or --max-forw-scroll=n
              Specifies a maximum number of lines to scroll forward.  If
              it is necessary to scroll forward more than n lines, the
              screen is repainted instead.  The -c or -C option may be
              used to repaint from the top of the screen if desired.  By
              default, any forward movement causes scrolling.

       -zn or --window=n or -n
              Changes the default scrolling window size to n lines.  The
              default is one screenful.  The z and w commands can also be
              used to change the window size.  The "z" may be omitted for
              compatibility with some versions of more(1).  If the number
              n is negative, it indicates n lines less than the current
              screen size.  For example, if the screen is 24 lines, -z-4
              sets the scrolling window to 20 lines.  If the screen is
              resized to 40 lines, the scrolling window automatically
              changes to 36 lines.

       -"cc or --quotes=cc
              Changes the filename quoting character.  This may be neces‐
              sary if you are trying to name a file which contains both
              spaces and quote characters.  Followed by a single charac‐
              ter, this changes the quote character to that character.
              Filenames containing a space should then be surrounded by
              that character rather than by double quotes.  Followed by
              two characters, changes the open quote to the first charac‐
              ter, and the close quote to the second character.  File‐
              names containing a space should then be preceded by the
              open quote character and followed by the close quote char‐
              acter.  Note that even after the quote characters are
              changed, this option remains -" (a dash followed by a dou‐
              ble quote).

       -~ or --tilde
              Normally lines after end of file are displayed as a single
              tilde (~).  This option causes lines after end of file to
              be displayed as blank lines.

       -# or --shift
              Specifies the default number of positions to scroll hori‐
              zontally in the RIGHTARROW and LEFTARROW commands.  If the
              number specified is zero, it sets the default number of po‐
              sitions to one half of the screen width.  Alternately, the
              number may be specified as a fraction of the width of the
              screen, starting with a decimal point: .5 is half of the
              screen width, .3 is three tenths of the screen width, and
              so on.  If the number is specified as a fraction, the actu‐
              al number of scroll positions is recalculated if the termi‐
              nal window is resized.

       --exit-follow-on-close
              When using the "F" command on a pipe, less will automati‐
              cally stop waiting for more data when the input side of the
              pipe is closed.

       --file-size
              If --file-size is specified, less will determine the size
              of the file immediately after opening the file.  Then the
              "=" command will display the number of lines in the file.
              Normally this is not done, because it can be slow if the
              input file is non-seekable (such as a pipe) and is large.

       --follow-name
              Normally, if the input file is renamed while an F command
              is executing, less will continue to display the contents of
              the original file despite its name change.  If --follow-
              name is specified, during an F command less will periodi‐
              cally attempt to reopen the file by name.  If the reopen
              succeeds and the file is a different file from the original
              (which means that a new file has been created with the same
              name as the original (now renamed) file), less will display
              the contents of that new file.

       --header=L,C,N
              Sets the number of header lines and columns displayed on
              the screen.  The number of header lines is set to L.  If L
              is 0, header lines are disabled.  If L is empty or missing,
              the number of header lines is unchanged.  The number of
              header columns is set to C.  If C is 0, header columns are
              disabled.  If C is empty or missing, the number of header
              columns is unchanged.  The first header line is set to line
              number N in the file.  If N is empty or missing, it is tak‐
              en to be the number of the line currently displayed in the
              first line of the screen (if the --header command has been
              issued from within less), or 1 (if the --header option has
              been given on the command line).  The special form "--head‐
              er=-" disables header lines and header columns, and is
              equivalent to "--header=0,0".

              When L is nonzero, the first L lines at the top of the
              screen are replaced with the L lines of the file beginning
              at line N, regardless of what part of the file is being
              viewed.  When header lines are displayed, any file contents
              before the header line cannot be viewed.  When C is nonze‐
              ro, the first C characters displayed at the beginning of
              each line are replaced with the first C characters of the
              line, even if the rest of the line is scrolled horizontal‐
              ly.

       --incsearch
              Subsequent search commands will be "incremental"; that is,
              less will advance to the next line containing the search
              pattern as each character of the pattern is typed in.

       --intr=c
              Use the character c instead of ^X to interrupt a read when
              the "Waiting for data" message is displayed.  c must be an
              ASCII character; that is, one with a value between 1 and
              127 inclusive.  A caret followed by a single character can
              be used to specify a control character.

       --line-num-width=n
              Sets the minimum width of the line number field when the -N
              option is in effect to n characters.  The default is 7.

       --match-shift=n
              When -S is in effect, if a search match is not visible be‐
              cause it is shifted to the left or right of the currently
              visible screen, the text will horizontally shift to ensure
              that the search match is visible.  This option selects the
              column in which the first character of the search match
              will be placed after the shift.  In other words, there will
              be n characters visible to the left of the search match.

              Alternately, the number may be specified as a fraction of
              the width of the screen, starting with a decimal point: .5
              is half of the screen width, .3 is three tenths of the
              screen width, and so on.  If the number is specified as a
              fraction, the actual number of scroll positions is recalcu‐
              lated if the terminal window is resized.

       --modelines=n
              Before displaying a file, less will read the first n lines
              to try to find a vim-compatible modeline.  If n is zero,
              less does not try to find modelines.  By using a modeline,
              the file itself can specify the tab stops that should be
              used when viewing it.

              A modeline contains, anywhere in the line, a program name
              ("vi", "vim", "ex", or "less"), followed by a colon, possi‐
              bly followed by the word "set", and finally followed by ze‐
              ro or more option settings.  If the word "set" is used, op‐
              tion settings are separated by spaces, and end at the first
              colon.  If the word "set" is not used, option settings may
              be separated by either spaces or colons.  The word "set" is
              required if the program name is "less" but optional if any
              of the other three names are used.  If any option setting
              is of the form "tabstop=n" or "ts=n", then tab stops are
              automatically set as if --tabs=n had been given.  See the
              --tabs description for acceptable values of n.

       --mouse
              Enables mouse input: scrolling the mouse wheel down moves
              forward in the file, scrolling the mouse wheel up moves
              backwards in the file, left-click sets the "#" mark to the
              line where the mouse is clicked, and right-click (or any
              other) returns to the "#" mark position.  If a left-click
              is performed with the mouse cursor on an OSC 8 hyperlink,
              the hyperlink is selected as if by the ^O^N command.  If a
              left-click is performed with the mouse cursor on an OSC 8
              hyperlink which is already selected, the hyperlink is
              opened as if by the ^O^O command.  The number of lines to
              scroll when the wheel is moved can be set by the --wheel-
              lines option.  Mouse input works only on terminals which
              support X11 mouse reporting, and on the Windows version of
              less.

       --MOUSE
              Like --mouse, except the direction scrolled on mouse wheel
              movement is reversed.

       --no-keypad
              Disables sending the keypad initialization and deinitial‐
              ization strings to the terminal.  This is sometimes useful
              if the keypad strings make the numeric keypad behave in an
              undesirable manner.

       --no-histdups
              This option changes the behavior so that if a search string
              or file name is typed in, and the same string is already in
              the history list, the existing copy is removed from the
              history list before the new one is added.  Thus, a given
              string will appear only once in the history list.  Normal‐
              ly, a string may appear multiple times.

       --no-number-headers
              Header lines (defined via the --header option) are not as‐
              signed line numbers.  Line number 1 is assigned to the
              first line after any header lines.

       --no-search-header-lines
              Searches do not include header lines, but still include
              header columns.

       --no-search-header-columns
              Searches do not include header columns, but still include
              header lines.

       --no-search-headers
              Searches do not include header lines or header columns.

       --no-vbell
              Disables the terminal's visual bell.

       --proc-backspace
              If set, backspaces are handled as if neither the -u option
              nor the -U option were set.  That is, a backspace adjacent
              to an underscore causes text to be displayed in underline
              mode, and a backspace between identical characters cause
              text to be displayed in boldface mode.  This option over‐
              rides the -u and -U options, so that display of backspaces
              can be controlled separate from tabs and carriage returns.
              If not set, backspace display is controlled by the -u and
              -U options.

       --PROC-BACKSPACE
              If set, backspaces are handled as if the -U option were
              set; that is backspaces are treated as control characters.

       --proc-return
              If set, carriage returns are handled as if neither the -u
              option nor the -U option were set.  That is, a carriage re‐
              turn immediately before a newline is deleted.  This option
              overrides the -u and -U options, so that display of car‐
              riage returns can be controlled separate from that of back‐
              spaces and tabs.  If not set, carriage return display is
              controlled by the -u and -U options.

       --PROC-RETURN
              If set, carriage returns are handled as if the -U option
              were set; that is carriage returns are treated as control
              characters.

       --proc-tab
              If set, tabs are handled as if the -U option were not set.
              That is, tabs are expanded to spaces.  This option over‐
              rides the -U option, so that display of tabs can be con‐
              trolled separate from that of backspaces and carriage re‐
              turns.  If not set, tab display is controlled by the -U op‐
              tions.

       --PROC-TAB
              If set, tabs are handled as if the -U option were set; that
              is tabs are treated as control characters.

       --redraw-on-quit
              When quitting, after sending the terminal deinitialization
              string, redraws the entire last screen.  On terminals whose
              terminal deinitialization string causes the terminal to
              switch from an alternate screen, this makes the last
              screenful of the current file remain visible after less has
              quit.

       --rscroll=c
              This option changes the character used to mark truncated
              lines.  It may begin with a two-character attribute indica‐
              tor like LESSBINFMT does.  If there is no attribute indica‐
              tor, standout is used.  If set to "-", truncated lines are
              not marked.

       --save-marks
              Save marks in the history file, so marks are retained
              across different invocations of less.

       --search-options=...
              Sets default search modifiers.  The value is a string of
              one or more of the characters E, F, K, N, R or W.  Setting
              any of these has the same effect as typing that control
              character at the beginning of every search pattern.  For
              example, setting --search-options=W is the same as typing
              ^W at the beginning of every pattern.  The value may also
              contain a digit between 1 and 5, which has the same effect
              as typing ^S followed by that digit at the beginning of
              every search pattern.  The value "-" disables all default
              search modifiers.

       --show-preproc-errors
              If a preprocessor produces data, then exits with a non-zero
              exit code, less will display a warning.

       --status-col-width=n
              Sets the width of the status column when the -J option is
              in effect.  The default is 2 characters.

       --status-line
              If a line is marked, the entire line (rather than just the
              status column) is highlighted.  Also lines highlighted due
              to the -w option will have the entire line highlighted.  If
              --use-color is set, the line is colored rather than high‐
              lighted.

       --use-backslash
              This option changes the interpretations of options which
              follow this one.  After the --use-backslash option, any
              backslash in an option string is removed and the following
              character is taken literally.  This allows a dollar sign to
              be included in option strings.

       --use-color
              Enables colored text in various places.  The -D option can
              be used to change the colors.  Colored text works only if
              the terminal supports ANSI color escape sequences (as de‐
              fined in
              https://www.ecma-international.org/publications-and-standards/standards/ecma-48).

       --wheel-lines=n
              Set the number of lines to scroll when the mouse wheel is
              scrolled and the --mouse or --MOUSE option is in effect.
              The default is 1 line.

       --wordwrap
              When the -S option is not in use, wrap each line at a space
              or tab if possible, so that a word is not split between two
              lines.  The default is to wrap at any character.

       --     A command line argument of "--" marks the end of option ar‐
              guments.  Any arguments following this are interpreted as
              filenames.  This can be useful when viewing a file whose
              name begins with a "-" or "+".

       +      If a command line option begins with +, the remainder of
              that option is taken to be an initial command to less.  For
              example, +G tells less to start at the end of the file
              rather than the beginning, and +/xyz tells it to start at
              the first occurrence of "xyz" in the file.  As a special
              case, +<number> acts like +<number>g; that is, it starts
              the display at the specified line number (however, see the
              caveat under the "g" command above).  If the option starts
              with ++, the initial command applies to every file being
              viewed, not just the first one.  The + command described
              previously may also be used to set (or change) an initial
              command for every file.

LINE EDITING

       When entering a command line at the bottom of the screen (for ex‐
       ample, a filename for the :e command, or the pattern for a search
       command), certain keys can be used to manipulate the command line.
       Most commands have an alternate form in [ brackets ] which can be
       used if a key does not exist on a particular keyboard.  (Note that
       the forms beginning with ESC do not work in some MS-DOS and Win‐
       dows systems because ESC is the line erase character.)  Any of
       these special keys may be entered literally by preceding it with
       the "literal" character, either ^V or ^A.  A backslash itself may
       also be entered literally by entering two backslashes.

       LEFTARROW [ ESC-h ]
              Move the cursor one space to the left.

       RIGHTARROW [ ESC-l ]
              Move the cursor one space to the right.

       ^LEFTARROW [ ESC-b or ESC-LEFTARROW ]
              (That is, CONTROL and LEFTARROW simultaneously.)  Move the
              cursor one word to the left.

       ^RIGHTARROW [ ESC-w or ESC-RIGHTARROW ]
              (That is, CONTROL and RIGHTARROW simultaneously.)  Move the
              cursor one word to the right.

       HOME [ ESC-0 ]
              Move the cursor to the beginning of the line.

       END [ ESC-$ ]
              Move the cursor to the end of the line.

       BACKSPACE
              Delete the character to the left of the cursor, or cancel
              the command if the command line is empty.

       DELETE or [ ESC-x ]
              Delete the character under the cursor.

       ^BACKSPACE [ ESC-BACKSPACE ]
              (That is, CONTROL and BACKSPACE simultaneously.)  Delete
              the word to the left of the cursor.

       ^DELETE [ ESC-X or ESC-DELETE ]
              (That is, CONTROL and DELETE simultaneously.)  Delete the
              word under the cursor.

       UPARROW [ ESC-k ]
              Retrieve the previous command line.  If you first enter
              some text and then press UPARROW, it will retrieve the pre‐
              vious command which begins with that text.

       DOWNARROW [ ESC-j ]
              Retrieve the next command line.  If you first enter some
              text and then press DOWNARROW, it will retrieve the next
              command which begins with that text.

       TAB    Complete the partial filename to the left of the cursor.
              If it matches more than one filename, the first match is
              entered into the command line.  Repeated TABs will cycle
              thru the other matching filenames.  If the completed file‐
              name is a directory, a "/" is appended to the filename.
              (On MS-DOS and Windows systems, a "\" is appended.)  The
              environment variable LESSSEPARATOR can be used to specify a
              different character to append to a directory name.

       BACKTAB [ ESC-TAB ]
              Like, TAB, but cycles in the reverse direction thru the
              matching filenames.

       ^L     Complete the partial filename to the left of the cursor.
              If it matches more than one filename, all matches are en‐
              tered into the command line (if they fit).

       ^U (Unix and OS/2) or ESC (MS-DOS and Windows)
              Delete the entire command line, or cancel the command if
              the command line is empty.  If you have changed your line-
              kill character in Unix to something other than ^U, that
              character is used instead of ^U.

       ^G     Delete the entire command line and return to the main
              prompt.

KEY BINDINGS

       You may define your own less commands by creating a lesskey source
       file.  This file specifies a set of command keys and an action as‐
       sociated with each key.  You may also change the line-editing keys
       (see LINE EDITING), and set environment variables used by less.
       See the lesskey(1) manual page for details about the file format.

       If the environment variable LESSKEYIN is set, less uses that as
       the name of the lesskey source file.  Otherwise, less looks in a
       standard place for the lesskey source file: On Unix systems, less
       looks for a lesskey file called "$XDG_CONFIG_HOME/lesskey" or
       "$HOME/.config/lesskey" or "$HOME/.lesskey".  On MS-DOS and Win‐
       dows systems, less looks for a lesskey file called
       "$HOME/_lesskey", and if it is not found there, then looks for a
       lesskey file called "_lesskey" in any directory specified in the
       PATH environment variable.  On OS/2 systems, less looks for a
       lesskey file called "$HOME/lesskey.ini", and if it is not found,
       then looks for a lesskey file called "lesskey.ini" in any directo‐
       ry specified in the INIT environment variable, and if it not found
       there, then looks for a lesskey file called "lesskey.ini" in any
       directory specified in the PATH environment variable.

       A system-wide lesskey source file may also be set up to provide
       key bindings.  If a key is defined in both a local lesskey file
       and in the system-wide file, key bindings in the local file take
       precedence over those in the system-wide file.  If the environment
       variable LESSKEYIN_SYSTEM is set, less uses that as the name of
       the system-wide lesskey file.  Otherwise, less looks in a standard
       place for the system-wide lesskey file: On Unix systems, the sys‐
       tem-wide lesskey file is /usr/local/etc/syslesskey.  (However, if
       less was built with a different sysconf directory than /usr/lo‐
       cal/etc, that directory is where the sysless file is found.)  On
       MS-DOS and Windows systems, the system-wide lesskey file is
       c:\_syslesskey.  On OS/2 systems, the system-wide lesskey file is
       c:\syslesskey.ini.

       Previous versions of less (before v582) used lesskey files with a
       binary format, produced by the lesskey program. It is no longer
       necessary to use the lesskey program.

INPUT PREPROCESSOR

       You may define an "input preprocessor" for less.  Before less
       opens a file, it first gives your input preprocessor a chance to
       modify the way the contents of the file are displayed.  An input
       preprocessor is simply an executable program (or shell script),
       which writes the contents of the file to a different file, called
       the replacement file.  The contents of the replacement file are
       then displayed in place of the contents of the original file.
       However, it will appear to the user as if the original file is
       opened; that is, less will display the original filename as the
       name of the current file.

       An input preprocessor receives one command line argument, the
       original filename, as entered by the user.  It should create the
       replacement file, and when finished, print the name of the re‐
       placement file to its standard output.  If the input preprocessor
       does not output a replacement filename, less uses the original
       file, as normal.  The input preprocessor is not called when view‐
       ing standard input.  To set up an input preprocessor, set the
       LESSOPEN environment variable to a command line which will invoke
       your input preprocessor.  This command line should include one oc‐
       currence of the string "%s", which will be replaced by the file‐
       name when the input preprocessor command is invoked.

       When less closes a file opened in such a way, it will call another
       program, called the input postprocessor, which may perform any de‐
       sired clean-up action (such as deleting the replacement file cre‐
       ated by LESSOPEN).  This program receives two command line argu‐
       ments, the original filename as entered by the user, and the name
       of the replacement file.  To set up an input postprocessor, set
       the LESSCLOSE environment variable to a command line which will
       invoke your input postprocessor.  It may include two occurrences
       of the string "%s"; the first is replaced with the original name
       of the file and the second with the name of the replacement file,
       which was output by LESSOPEN.

       For example, on many Unix systems, these two scripts will allow
       you to keep files in compressed format, but still let less view
       them directly:

       lessopen.sh:
            #! /bin/sh
            case "$1" in
            *.Z) TEMPFILE=$(mktemp)
                 uncompress -c $1  >$TEMPFILE  2>/dev/null
                 if [ -s $TEMPFILE ]; then
                      echo $TEMPFILE
                 else
                      rm -f $TEMPFILE
                 fi
                 ;;
            esac

       lessclose.sh:
            #! /bin/sh
            rm $2

       To use these scripts, put them both where they can be executed and
       set LESSOPEN="lessopen.sh %s", and LESSCLOSE="lessclose.sh %s %s".
       More complex LESSOPEN and LESSCLOSE scripts may be written to ac‐
       cept other types of compressed files, and so on.

       It is also possible to set up an input preprocessor to pipe the
       file data directly to less, rather than putting the data into a
       replacement file.  This avoids the need to decompress the entire
       file before starting to view it.  An input preprocessor that works
       this way is called an input pipe.  An input pipe, instead of writ‐
       ing the name of a replacement file on its standard output, writes
       the entire contents of the replacement file on its standard out‐
       put.  If the input pipe does not write any characters on its stan‐
       dard output, then there is no replacement file and less uses the
       original file, as normal.  To use an input pipe, make the first
       character in the LESSOPEN environment variable a vertical bar (|)
       to signify that the input preprocessor is an input pipe.  As with
       non-pipe input preprocessors, the command string must contain one
       occurrence of %s, which is replaced with the filename of the input
       file.

       For example, on many Unix systems, this script will work like the
       previous example scripts:

       lesspipe.sh:
            #! /bin/sh
            case "$1" in
            *.Z) uncompress -c $1  2>/dev/null
                 ;;
            *)   exit 1
                 ;;
            esac
            exit $?

       To use this script, put it where it can be executed and set
       LESSOPEN="|lesspipe.sh %s".

       Note that a preprocessor cannot output an empty file, since that
       is interpreted as meaning there is no replacement, and the origi‐
       nal file is used.  To avoid this, if LESSOPEN starts with two ver‐
       tical bars, the exit status of the script determines the behavior
       when the output is empty.  If the output is empty and the exit
       status is zero, the empty output is considered to be replacement
       text.  If the output is empty and the exit status is nonzero, the
       original file is used.  For compatibility with previous versions
       of less, if LESSOPEN starts with only one vertical bar, the exit
       status of the preprocessor is ignored.

       When an input pipe is used, a LESSCLOSE postprocessor can be used,
       but it is usually not necessary since there is no replacement file
       to clean up.  In this case, the replacement file name passed to
       the LESSCLOSE postprocessor is "-".

       For compatibility with previous versions of less, the input pre‐
       processor or pipe is not used if less is viewing standard input.
       However, if the first character of LESSOPEN is a dash (-), the in‐
       put preprocessor is used on standard input as well as other files.
       In this case, the dash is not considered to be part of the pre‐
       processor command.  If standard input is being viewed, the input
       preprocessor is passed a file name consisting of a single dash.
       Similarly, if the first two characters of LESSOPEN are vertical
       bar and dash (|-) or two vertical bars and a dash (||-), the input
       pipe is used on standard input as well as other files.  Again, in
       this case the dash is not considered to be part of the input pipe
       command.

NATIONAL CHARACTER SETS

       There are three types of characters in the input file:

       normal characters
              can be displayed directly to the screen.

       control characters
              should not be displayed directly, but are expected to be
              found in ordinary text files (such as backspace and tab).

       binary characters
              should not be displayed directly and are not expected to be
              found in text files.

       A "character set" is simply a description of which characters are
       to be considered normal, control, and binary.  The LESSCHARSET en‐
       vironment variable may be used to select a character set.  Possi‐
       ble values for LESSCHARSET are:

       ascii  BS, TAB, NL, CR, and formfeed are control characters, all
              chars with values between 32 and 126 are normal, and all
              others are binary.

       iso8859
              Selects an ISO 8859 character set.  This is the same as
              ASCII, except characters between 160 and 255 are treated as
              normal characters.

       latin1 Same as iso8859.

       latin9 Same as iso8859.

       dos    Selects a character set appropriate for MS-DOS.

       ebcdic Selects an EBCDIC character set.

       IBM-1047
              Selects an EBCDIC character set used by OS/390 Unix Ser‐
              vices.  This is the EBCDIC analogue of latin1.  You get
              similar results by setting either LESSCHARSET=IBM-1047 or
              LC_CTYPE=en_US in your environment.

       koi8-r Selects a Russian character set.

       next   Selects a character set appropriate for NeXT computers.

       utf-8  Selects the UTF-8 encoding of the ISO 10646 character set.
              UTF-8 is special in that it supports multi-byte characters
              in the input file.  It is the only character set that sup‐
              ports multi-byte characters.

       windows
              Selects a character set appropriate for Microsoft Windows
              (cp 1252).

       In rare cases, it may be desired to tailor less to use a character
       set other than the ones definable by LESSCHARSET.  In this case,
       the environment variable LESSCHARDEF can be used to define a char‐
       acter set.  It should be set to a string where each character in
       the string represents one character in the character set.  The
       character "." is used for a normal character, "c" for control, and
       "b" for binary.  A decimal number may be used for repetition.  For
       example, "bccc4b." would mean character 0 is binary, 1, 2 and 3
       are control, 4, 5, 6 and 7 are binary, and 8 is normal.  All char‐
       acters after the last are taken to be the same as the last, so
       characters 9 through 255 would be normal.  (This is an example,
       and does not necessarily represent any real character set.)

       This table shows the value of LESSCHARDEF which is equivalent to
       each of the possible values for LESSCHARSET:
            ascii      8bcccbcc18b95.b
            dos        8bcccbcc12bc5b95.b.
            ebcdic     5bc6bcc7bcc41b.9b7.9b5.b..8b6.10b6.b9.7b
                       9.8b8.17b3.3b9.7b9.8b8.6b10.b.b.b.
            IBM-1047   4cbcbc3b9cbccbccbb4c6bcc5b3cbbc4bc4bccbc
                       191.b
            iso8859    8bcccbcc18b95.33b.
            koi8-r     8bcccbcc18b95.b128.
            latin1     8bcccbcc18b95.33b.
            next       8bcccbcc18b95.bb125.bb

       If neither LESSCHARSET nor LESSCHARDEF is set, but any of the
       strings "UTF-8", "UTF8", "utf-8" or "utf8" is found in the LC_ALL,
       LC_CTYPE or LANG environment variables, then the default character
       set is utf-8.

       If that string is not found, but your system supports the setlo‐
       cale interface, less will use setlocale to determine the character
       set.  setlocale is controlled by setting the LANG or LC_CTYPE en‐
       vironment variables.

       Finally, if the setlocale interface is also not available, the de‐
       fault character set is utf-8.

       Control and binary characters are displayed in standout (reverse
       video).  Each such character is displayed in caret notation if
       possible (e.g. ^A for control-A).  Caret notation is used only if
       inverting the 0100 bit results in a normal printable character.
       Otherwise, the character is displayed as a hex number in angle
       brackets.  This format can be changed by setting the LESSBINFMT
       environment variable.  LESSBINFMT may begin with a "*" and one
       character to select the display attribute: "*k" is blinking, "*d"
       is bold, "*u" is underlined, "*s" is standout, and "*n" is normal.
       If LESSBINFMT does not begin with a "*", normal attribute is as‐
       sumed.  The remainder of LESSBINFMT is a string which may include
       one printf-style escape sequence (a % followed by x, X, o, d,
       etc.).  For example, if LESSBINFMT is "*u[%x]", binary characters
       are displayed in underlined hexadecimal surrounded by brackets.
       The default if no LESSBINFMT is specified is "*s<%02X>".  Warning:
       the result of expanding the character via LESSBINFMT must be less
       than 31 characters.

       When the character set is utf-8, the LESSUTFBINFMT environment
       variable acts similarly to LESSBINFMT but it applies to Unicode
       code points that were successfully decoded but are unsuitable for
       display (e.g., unassigned code points).  Its default value is
       "<U+%04lX>".  Note that LESSUTFBINFMT and LESSBINFMT share their
       display attribute setting ("*x") so specifying one will affect
       both; LESSUTFBINFMT is read after LESSBINFMT so its setting, if
       any, will have priority.  Problematic octets in a UTF-8 file
       (octets of a truncated sequence, octets of a complete but non-
       shortest form sequence, invalid octets, and stray trailing octets)
       are displayed individually using LESSBINFMT so as to facilitate
       diagnostic of how the UTF-8 file is ill-formed.

       When the character set is utf-8, in rare cases it may be desirable
       to override the Unicode definition of the type of certain charac‐
       ters.  For example, characters in a Private Use Area are normally
       treated as control characters, but if you are using a custom font
       with printable characters in that range, it may be desirable to
       tell less to treat such characters as printable.  This can be done
       by setting the LESSUTFCHARDEF environment variable to a comma-sep‐
       arated list of character type definitions.  Each character type
       definition consists of either one hexadecimal codepoint or a pair
       of codepoints separated by a dash, followed by a colon and a type
       character.  Each hexadecimal codepoint may optionally be preceded
       by a "U" or "U+".  If a pair of codepoints is given, the type is
       set for all characters inclusively between the two values.  If
       there are multiple comma-separated codepoint values, they must be
       in ascending numerical order.  The type character may be one of:

              p      A normal printable character.

              w      A wide (2-space) printable character.

              b      A binary (non-printable) character.

              c      A composing (zero width) character.

       For example, setting LESSUTFCHARDEF to

            E000-F8FF:p,F0000-FFFFD:p,100000-10FFFD:p

       would make all Private Use Area characters be treated as print‐
       able.

PROMPTS

       The -P option allows you to tailor the prompt to your preference.
       The string given to the -P option replaces the specified prompt
       string.  Certain characters in the string are interpreted special‐
       ly.  The prompt mechanism is rather complicated to provide flexi‐
       bility, but the ordinary user need not understand the details of
       constructing personalized prompt strings.

       A percent sign followed by a single character is expanded accord‐
       ing to what the following character is.  (References to the input
       file size below refer to the preprocessed size, if an input pre‐
       processor is being used.)

       %bX    Replaced by the byte offset into the current input file.
              The b is followed by a single character (shown as X above)
              which specifies the line whose byte offset is to be used.
              If the character is a "t", the byte offset of the top line
              in the display is used, an "m" means use the middle line, a
              "b" means use the bottom line, a "B" means use the line
              just after the bottom line, and a "j" means use the "tar‐
              get" line, as specified by the -j option.

       %B     Replaced by the size of the current input file.

       %c     Replaced by the column number of the text appearing in the
              first column of the screen.

       %dX    Replaced by the page number of a line in the input file.
              The line to be used is determined by the X, as with the %b
              option.

       %D     Replaced by the number of pages in the input file, or
              equivalently, the page number of the last line in the input
              file.

       %E     Replaced by the name of the editor (from the VISUAL envi‐
              ronment variable, or the EDITOR environment variable if VI‐
              SUAL is not defined).  See the discussion of the LESSEDIT
              feature below.

       %f     Replaced by the name of the current input file.

       %F     Replaced by the last component of the name of the current
              input file.

       %g     Replaced by the shell-escaped name of the current input
              file.  This is useful when the expanded string will be used
              in a shell command, such as in LESSEDIT.

       %i     Replaced by the index of the current file in the list of
              input files.

       %lX    Replaced by the line number of a line in the input file.
              The line to be used is determined by the X, as with the %b
              option.

       %L     Replaced by the line number of the last line in the input
              file.

       %m     Replaced by the total number of input files.

       %o     Replaced by the URI of the currently selected OSC 8 hyper‐
              link, or a question mark if no hyperlink is selected.  This
              is used by OSC 8 handlers as explained in the ^O^O command
              description.

       %pX    Replaced by the percent into the current input file, based
              on byte offsets.  The line used is determined by the X as
              with the %b option.

       %PX    Replaced by the percent into the current input file, based
              on line numbers.  The line used is determined by the X as
              with the %b option.

       %s     Same as %B.

       %t     Causes any trailing spaces to be removed.  Usually used at
              the end of the string, but may appear anywhere.

       %T     Normally expands to the word "file".  However if viewing
              files via a tags list using the -t option, it expands to
              the word "tag".

       %x     Replaced by the name of the next input file in the list.

       If any item is unknown (for example, the file size if input is a
       pipe), a question mark is printed instead.

       The format of the prompt string can be changed depending on cer‐
       tain conditions.  A question mark followed by a single character
       acts like an "IF": depending on the following character, a condi‐
       tion is evaluated.  If the condition is true, any characters fol‐
       lowing the question mark and condition character, up to a period,
       are included in the prompt.  If the condition is false, such char‐
       acters are not included.  A colon appearing between the question
       mark and the period can be used to establish an "ELSE": any char‐
       acters between the colon and the period are included in the string
       if and only if the IF condition is false.  Condition characters
       (which follow a question mark) may be:

       ?a     True if any characters have been included in the prompt so
              far.

       ?bX    True if the byte offset of the specified line is known.

       ?B     True if the size of current input file is known.

       ?c     True if the text is horizontally shifted (%c is not zero).

       ?dX    True if the page number of the specified line is known.

       ?e     True if at end-of-file.

       ?f     True if there is an input filename (that is, if input is
              not a pipe).

       ?lX    True if the line number of the specified line is known.

       ?L     True if the line number of the last line in the file is
              known.

       ?m     True if there is more than one input file.

       ?n     True if this is the first prompt in a new input file.

       ?pX    True if the percent into the current input file, based on
              byte offsets, of the specified line is known.

       ?PX    True if the percent into the current input file, based on
              line numbers, of the specified line is known.

       ?s     Same as "?B".

       ?x     True if there is a next input file (that is, if the current
              input file is not the last one).

       Any characters other than the special ones (question mark, colon,
       period, percent, and backslash) become literally part of the
       prompt.  Any of the special characters may be included in the
       prompt literally by preceding it with a backslash.

       Some examples:

       ?f%f:Standard input.

       This prompt prints the filename, if known; otherwise the string
       "Standard input".

       ?f%f .?ltLine %lt:?pt%pt\%:?btByte %bt:-...

       This prompt would print the filename, if known.  The filename is
       followed by the line number, if known, otherwise the percent if
       known, otherwise the byte offset if known.  Otherwise, a dash is
       printed.  Notice how each question mark has a matching period, and
       how the % after the %pt is included literally by escaping it with
       a backslash.

       ?n?f%f .?m(%T %i of %m) ..?e(END) ?x- Next\: %x..%t

       This prints the filename if this is the first prompt in a file,
       followed by the "file N of N" message if there is more than one
       input file.  Then, if we are at end-of-file, the string "(END)" is
       printed followed by the name of the next file, if there is one.
       Finally, any trailing spaces are truncated.  This is the default
       prompt.  For reference, here are the defaults for the other two
       prompts (-m and -M respectively).  Each is broken into two lines
       here for readability only.

       ?n?f%f .?m(%T %i of %m) ..?e(END) ?x- Next\: %x.:
            ?pB%pB\%:byte %bB?s/%s...%t

       ?f%f .?n?m(%T %i of %m) ..?ltlines %lt-%lb?L/%L. :
            byte %bB?s/%s. .?e(END) ?x- Next\: %x.:?pB%pB\%..%t

       And here is the default message produced by the = command:

       ?f%f .?m(%T %i of %m) .?ltlines %lt-%lb?L/%L. .
            byte %bB?s/%s. ?e(END) :?pB%pB\%..%t

       The prompt expansion features are also used for another purpose:
       if an environment variable LESSEDIT is defined, it is used as the
       command to be executed when the v command is invoked.  The LESSED‐
       IT string is expanded in the same way as the prompt strings.  The
       default value for LESSEDIT is:

            %E ?lm+%lm. %g

       Note that this expands to the editor name, followed by a + and the
       line number, followed by the shell-escaped file name.  If your ed‐
       itor does not accept the "+linenumber" syntax, or has other dif‐
       ferences in invocation syntax, the LESSEDIT variable can be
       changed to modify this default.

SECURITY

       When the environment variable LESSSECURE is set to 1, less runs in
       a "secure" mode.  In this mode, these features are disabled:

       edit      the edit command (v)

       examine   the examine command (:e)

       glob      metacharacters such as * in filenames,
                 and filename completion (TAB, ^L)

       history   history file

       lesskey   use of lesskey files (-k and --lesskey-src)

       lessopen  input preprocessor (LESSOPEN environment variable)

       logfile   log files (s and -o)

       osc8      opening OSC 8 links (^O^O)

       pipe      the pipe command (|)

       shell     the shell and pshell commands (! and #)

       stop      stopping less via a SIGSTOP signal

       tags      use of tags files (-t)

       The LESSSECURE_ALLOW environment variable can be set to a comma-
       separated list of names of features which are selectively enabled
       when LESSSECURE is set.  Each feature name is the first word in
       each line in the above list.  A feature name may be abbreviated as
       long as the abbreviation is unambiguous.  For example, if
       LESSSECURE=1 and LESSSECURE_ALLOW=hist,edit were set, all of the
       above features would be disabled except for history files and the
       edit command.

       Less can also be compiled to be permanently in "secure" mode.  In
       that case, the LESSSECURE and LESSSECURE_ALLOW variables are ig‐
       nored.

COMPATIBILITY WITH MORE

       If the environment variable LESS_IS_MORE is set to 1, or if the
       program is invoked via a file link named "more", less behaves
       (mostly) in conformance with the POSIX more(1) command specifica‐
       tion.  In this mode, less behaves differently in these ways:

       The -e option works differently.  If the -e option is not set,
       less behaves as if the -e option were set.  If the -e option is
       set, less behaves as if the -E option were set.

       The -m option works differently.  If the -m option is not set, the
       medium prompt is used, and it is prefixed with the string
       "--More--".  If the -m option is set, the short prompt is used.

       The -n option acts like the -z option.  The normal behavior of the
       -n option is unavailable in this mode.

       The parameter to the -p option is taken to be a less command
       rather than a search pattern.

       The LESS environment variable is ignored, and the MORE environment
       variable is used in its place.

ENVIRONMENT VARIABLES

       Environment variables may be specified either in the system envi‐
       ronment as usual, or in a lesskey(1) file.  If environment vari‐
       ables are defined in more than one place, variables defined in a
       local lesskey file take precedence over variables defined in the
       system environment, which take precedence over variables defined
       in the system-wide lesskey file.

       COLUMNS
              Sets the number of columns on the screen.  Takes precedence
              over the number of columns specified by the TERM variable.
              (But if you have a windowing system which supports TIOCG‐
              WINSZ or WIOCGETD, the window system's idea of the screen
              size takes precedence over the LINES and COLUMNS environ‐
              ment variables.)

       EDITOR The name of the editor (used for the v command).

       HOME   Name of the user's home directory (used to find a lesskey
              file on Unix and OS/2 systems).

       HOMEDRIVE, HOMEPATH
              Concatenation of the HOMEDRIVE and HOMEPATH environment
              variables is the name of the user's home directory if the
              HOME variable is not set (only in the Windows version).

       INIT   Name of the user's init directory (used to find a lesskey
              file on OS/2 systems).

       LANG   Language for determining the character set.

       LC_CTYPE
              Language for determining the character set.

       LESS   Options which are passed to less automatically.

       LESSANSIENDCHARS
              Characters which may end an ANSI color escape sequence (de‐
              fault "m").

       LESSANSIMIDCHARS
              Characters which may appear between the ESC character and
              the end character in an ANSI color escape sequence (default
              "0123456789:;[?!"'#%()*+ ".

       LESSBINFMT
              Format for displaying non-printable, non-control charac‐
              ters.

       LESSCHARDEF
              Defines a character set.

       LESSCHARSET
              Selects a predefined character set.

       LESSCLOSE
              Command line to invoke the (optional) input-postprocessor.

       LESSECHO
              Name of the lessecho program (default "lessecho").  The
              lessecho program is needed to expand metacharacters, such
              as * and ?, in filenames on Unix systems.

       LESSEDIT
              Editor prototype string (used for the v command).  See dis‐
              cussion under PROMPTS.

       LESSGLOBALTAGS
              Name of the command used by the -t option to find global
              tags.  Normally should be set to "global" if your system
              has the global(1) command.  If not set, global tags are not
              used.

       LESSHISTFILE
              Name of the history file used to remember search commands
              and shell commands between invocations of less.  If set to
              "-" or "/dev/null", a history file is not used.  The de‐
              fault depends on the operating system, but is usually:

              Linux and Unix
                     "$XDG_STATE_HOME/lesshst" or "$HOME/.lo‐
                     cal/state/lesshst" or "$XDG_DATA_HOME/lesshst" or
                     "$HOME/.lesshst".

              Windows and MS-DOS
                     "$HOME/_lesshst".

              OS/2   "$HOME/lesshst.ini" or "$INIT/lesshst.ini".

       LESSHISTSIZE
              The maximum number of commands to save in the history file.
              The default is 100.

       LESSKEYIN
              Name of the default lesskey source file.

       LESSKEY
              Name of the default lesskey binary file. (Not used if
              "$LESSKEYIN" exists.)

       LESSKEY_CONTENT
              The value is parsed as if it were the parameter of a
              --lesskey-content option.

       LESSKEYIN_SYSTEM
              Name of the default system-wide lesskey source file.

       LESSKEY_SYSTEM
              Name of the default system-wide lesskey binary file. (Not
              used if "$LESSKEYIN_SYSTEM" exists.)

       LESSMETACHARS
              List of characters which are considered "metacharacters" by
              the shell.

       LESSMETAESCAPE
              Prefix which less will add before each metacharacter in a
              command sent to the shell.  If LESSMETAESCAPE is an empty
              string, commands containing metacharacters will not be
              passed to the shell.

       LESSOPEN
              Command line to invoke the (optional) input-preprocessor.

       LESSSECURE
              Runs less in "secure" mode.  See discussion under SECURITY.

       LESSSECURE_ALLOW
              Enables individual features which are normally disabled by
              LESSSECURE.  See discussion under SECURITY.

       LESSSEPARATOR
              String to be appended to a directory name in filename com‐
              pletion.

       LESSUTFBINFMT
              Format for displaying non-printable Unicode code points.

       LESSUTFCHARDEF
              Overrides the type of specified Unicode characters.

       LESS_COLUMNS
              Sets the number of columns on the screen.  Unlike COLUMNS,
              takes precedence over the system's idea of the screen size,
              so it can be used to make less use less than the full
              screen width.  If set to a negative number, sets the number
              of columns used to this much less than the actual screen
              width.

       LESS_LINES
              Sets the number of lines on the screen.  Unlike LINES,
              takes precedence over the system's idea of the screen size,
              so it can be used to make less use less than the full
              screen height.  If set to a negative number, sets the num‐
              ber of lines used to this much less than the actual screen
              height.  When set, less repaints the entire screen on every
              movement command, so scrolling may be slower.

       LESS_DATA_DELAY
              Duration (in milliseconds) after starting to read data from
              the input, after which the "Waiting for data" message will
              be displayed.  The default is 4000 (4 seconds).

       LESS_IS_MORE
              Emulate the more(1) command.

       LESS_OSC8_xxx
              Where "xxx" is a URI scheme such as "http" or "file", sets
              an OSC 8 handler for opening OSC 8 links containing a URI
              with that scheme.

       LESS_OSC8_ANY
              Sets an OSC 8 handler for opening OSC 8 links for which
              there is no specific LESS_OSC8_xxx handler set for the
              "xxx" scheme.

       LESS_TERMCAP_xx
              Where "xx" is any two characters, overrides the definition
              of the termcap "xx" capability for the terminal.

       LESS_UNSUPPORT
              A space-separated list of command line options.  These op‐
              tions will be ignored (with no error message) if they ap‐
              pear on the command line or in the LESS environment vari‐
              able.  Options listed in LESS_UNSUPPORT can still be
              changed by the - and -- commands.  Each option in LESS_UN‐
              SUPPORT is a dash followed by a single character option
              letter, or two dashes followed by a long option name.

       LINES  Sets the number of lines on the screen.  Takes precedence
              over the number of lines specified by the TERM variable.
              (But if you have a windowing system which supports TIOCG‐
              WINSZ or WIOCGETD, the window system's idea of the screen
              size takes precedence over the LINES and COLUMNS environ‐
              ment variables.)

       MORE   Options which are passed to less automatically when running
              in more-compatible mode.

       PATH   User's search path (used to find a lesskey file on MS-DOS,
              Windows, and OS/2 systems).

       SHELL  The shell used to execute the ! command, as well as to ex‐
              pand filenames.

       TERM   The type of terminal on which less is being run.

       VISUAL The name of the editor (used for the v command).

       XDG_CONFIG_HOME
              Possible location of the lesskey file; see the KEY BINDINGS
              section.

       XDG_DATA_HOME
              Possible location of the history file; see the description
              of the LESSHISTFILE environment variable.

       XDG_STATE_HOME
              Possible location of the history file; see the description
              of the LESSHISTFILE environment variable.

SEE ALSO

       lesskey(1), lessecho(1)

COPYRIGHT

       Copyright (C) 1984-2024  Mark Nudelman

       less is part of the GNU project and is free software.  You can re‐
       distribute it and/or modify it under the terms of either (1) the
       GNU General Public License as published by the Free Software Foun‐
       dation; or (2) the Less License.  See the file README in the less
       distribution for more details regarding redistribution.  You
       should have received a copy of the GNU General Public License
       along with the source for less; see the file COPYING.  If not,
       write to the Free Software Foundation, 59 Temple Place, Suite 330,
       Boston, MA  02111-1307, USA.  You should also have received a copy
       of the Less License; see the file LICENSE.

       less is distributed in the hope that it will be useful, but WITH‐
       OUT ANY WARRANTY; without even the implied warranty of MER‐
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
       General Public License for more details.

AUTHOR

       Mark Nudelman
       Report bugs at https://github.com/gwsw/less/issues.
       For more information, see the less homepage at
       https://greenwoodsoftware.com/less.

COLOPHON

       This page is part of the less (A file pager) project.  Information
       about the project can be found at 
       ⟨http://www.greenwoodsoftware.com/less/⟩.  If you have a bug report
       for this manual page, see
       ⟨http://www.greenwoodsoftware.com/less/faq.html#bugs⟩.  This page
       was obtained from the tarball less-668.tar.gz fetched from
       ⟨http://www.greenwoodsoftware.com/less/download.html⟩ on
       2024-02-02.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org