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命令用途

watch 命令用于定期（默认2秒间隔）执行指定命令，并全屏显示输出结果，适合监控命令输出的动态变化。

常用用法示例

  1. 默认间隔（2秒）执行命令

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    watch date
    Every 2.0s: date hostname: Wed Jun 12 15:30:00 2024
    Wed Jun 12 15:30:00 CST 2024

    实时显示当前时间，每2秒刷新一次。

  2. 指定刷新间隔（5秒）

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    watch -n 5 free -h
    Every 5.0s: free -h hostname: Wed Jun 12 15:30:05 2024
    total used free shared buff/cache available
    Mem: 7.7G 2.1G 3.2G 200M 2.4G 5.2G
    Swap: 2.0G 0B 2.0G

    每5秒刷新一次内存使用情况。

  3. 高亮显示输出变化

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    watch -d ls -l
    Every 2.0s: ls -l hostname: Wed Jun 12 15:30:10 2024
    total 8
    -rw-r--r-- 1 user user 0 Jun 12 15:30 new_file.txt

    当目录内文件变化时，变化的行会高亮显示。

  4. 当输出变化时自动退出

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watch -g "ls | grep 'error.log'"
（当目录中出现 error.log 文件时，watch 自动退出）

监控目录，一旦出现 error.log 文件即停止监控。

  1. 隐藏顶部状态栏

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    watch -t "uptime"
    15:30:15 up 1 day, 3:22, 2 users, load average: 0.08, 0.03, 0.01

    隐藏时间、命令和主机名等头部信息。

  2. 精确到秒的小数间隔

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watch -n 0.5 "ps aux | grep python"
Every 0.5s: ps aux | grep python hostname: Wed Jun 12 15:30:20 2024
user 1234 0.0 0.1 12345 6789 pts/0 S+ 15:30 0:00 python script.py

每0.5秒刷新一次，监控 Python 进程。

  1. 结合管道和复杂命令

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    watch "echo '当前连接数：' && netstat -an | grep ':80 ' | wc -l"
    Every 2.0s: echo '当前连接数：' && netstat -an | grep ':80 ' | wc -l
    当前连接数：
    12

    每2秒统计一次80端口的连接数。

  2. 执行命令后发出蜂鸣声

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    watch -b "ls /tmp/lockfile"
    Every 2.0s: ls /tmp/lockfile hostname: Wed Jun 12 15:30:25 2024
    ls: cannot access '/tmp/lockfile': No such file or directory

    当命令执行失败（如文件不存在）时，终端发出蜂鸣声。

常用参数选项

  • -n <秒>, –interval <秒>
    设置刷新间隔时间（默认2秒），支持小数（如 -n 0.5）。
  • -d, –differences
    高亮显示本次输出与上一次的变化部分。
  • –color
    与 -d 结合使用时，使用颜色高亮变化（需终端支持）。
  • -g, –chgexit
    当命令输出发生变化时，watch 自动退出。
  • -t, –no-title
    隐藏顶部状态栏（时间、命令和主机名）。
  • -b, –beep
    当命令的退出状态码非零时，发出蜂鸣声。
  • -e, –errexit
    命令执行错误（非零退出码）时停止刷新并退出。
  • -p, –precise
    精确计时模式，尝试抵消执行命令本身的时间消耗。

原厂文档

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NAME

       watch - execute a program periodically, showing output fullscreen

SYNOPSIS

       watch [option ...] command

DESCRIPTION

       watch runs command repeatedly, displaying its output and errors
       (the first screenful). This allows you to watch the program output
       change over time. By default, command is run every 2 seconds and
       watch will run until interrupted.  A header informs of the start
       and running time of command as well as its exit code.

OPTIONS

       -b, --beep
              Beep if command has a non-zero exit.

       -c, --color
              Interpret ANSI color and style sequences.

       -C, --no-color
              Do not interpret ANSI color and style sequences.

       -d, --differences[=permanent]
              Highlight the differences between successive updates. If
              the optional permanent argument is specified then watch
              will show all changes since the first iteration.

       -e, --errexit
              Freeze updates on command error, and exit after a key
              press. The exit code of watch will be the code command
              exits with. If signal n is the cause of command
              termination, the exit code will be 128 + n.

       -g, --chgexit
              Exit when the visible output of command changes. Changes
              that are off the screen due to small screen size or large
              output will not cause watch to exit.

       -n, --interval seconds
              Specify update interval. Values smaller than 0.1 and larger
              than 2678400 (31 days) are converted into these respective
              bounds. Both '.' and ',' work for any locale. The
              WATCH_INTERVAL environment variable can be used to
              persistently set a non-default interval (following the same
              rules and formatting).

       -p, --precise
              Execute command --interval seconds after its previous run
              started, instead of --interval seconds after its previous
              run finished. If it's taking longer than --interval seconds
              for command to complete, it is waited for in either case.

       -q, --equexit <cycles>
              Exit when output of command does not change for the given
              number of cycles.

       -r, --no-rerun
              Do not run the program on terminal resize, the output of
              the program will re-appear at the next regular run time.

       -s, --shotsdir
              Directory to save screenshots into.

       -t, --no-title
              Turn off the header normally shown at the top of the
              screen.

       -w, --no-wrap
              Turn off line wrapping. Long lines will be truncated
              instead of wrapped to the next line.

       -x, --exec
              Pass command to an exec(3) call instead of sh -c. The
              program will start a bit quicker. Shell features
              (environment setup, variable and pathname expansion, etc.)
              will be unavailable.

       -h, --help
              Display help text and exit.

       -v, --version
              Display version information and exit.

KEY CONTROL

       spacebar
              Issue command immediately. If it's running at the moment,
              it is not interrupted and its next round will start without
              delay.

       q      Quit watch. It currently does not interrupt a running
              command (as opposed to terminating signals, such as the
              SIGKILL following Ctrl+C).

       s      Take a screenshot. It will be saved in the working
              directory, unless specified otherwise by --shotsdir. If
              command is running at the moment, the screenshot will be
              taken as soon as it finishes.

EXIT STATUS

       0      Success. Does not represent command exit code.

       1      Errors unrelated to command operation.

       2      Errors related to command execution and management (not its
              exit code).

       any non-zero (--errexit)
              With --errexit the last exit code of command is returned.

ENVIRONMENT

       The behavior of watch is affected by the following environment
       variables.

       WATCH_INTERVAL
              Update interval, follows the same rules as the --interval
              command line option.

       COLUMNS
              Terminal screen character width. Set to override
              autodetection.

       LINES  Terminal screen character height. Set to override
              autodetection.

NOTES

       POSIX option processing is used (i.e., option processing stops at
       the first non-option argument). This means that flags after
       command don't get interpreted by watch itself.

       Non-printing characters are stripped from program output. Use cat
       -v as part of the command pipeline if you want to see them.

EXAMPLES

       To watch the contents of a directory change, you could use

              watch -d ls -l

       If you have CPUs with a dynamic frequency and want to observe it
       change, try the following. The command is passed to the shell,
       which allows you to make the pipeline. The quotes are a feature of
       the shell too.

              watch -n1 'grep "^cpu MHz" /proc/cpuinfo | sort -nrk4'

       To monitor the up status of your servers, saving a copy of the
       output of each run to a file, you may use this. The -p makes the
       command execute every 10 seconds regardless of how long it took to
       complete the previous run.

              watch -n10 -p -d '{ date; for i in 10.0.0.31 10.0.0.32
              10.0.0.33; do R=OK; ping -c2 -W2 "$i" &>/dev/null ||
              R=FAIL; echo "$i: $R"; done } | tee -a ~/log'

       You can watch for your administrator to install the latest kernel
       with

              watch uname -r

BUGS

       When the terminal dimensions change, its contents changes are not
       registered on the next command run. --chgexit will not trigger
       that turn and the counter of --equexit will not restart even if
       command output changes meanwhile. --differences highlighting is
       reset.

REPORTING BUGS

       Please send bug reports to ⟨procps@freelists.org⟩.

COLOPHON

       This page is part of the procps-ng (/proc filesystem utilities)
       project.  Information about the project can be found at 
       ⟨https://gitlab.com/procps-ng/procps⟩.  If you have a bug report
       for this manual page, see
       ⟨https://gitlab.com/procps-ng/procps/blob/master/Documentation/bugs.md⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://gitlab.com/procps-ng/procps.git⟩ on 2024-02-02.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-01-15.)  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