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watch命令可以反复的执行一个命令，默认时间间隔为2秒钟。
watch ifconfig 可以每隔两秒监视网络状态、
watch -d ifconfig 可以每隔两秒监视网络状态, 并标记发生变化的部分
watch -d ifconfig eth0 可以每隔两秒只监视 网卡eth0, 并标记发生变化的部分
watch -d 'ifconfig eth0 | grep bytes' 可以每隔一秒只监视网卡eth0,只显示流量部分,并标记发生变化的部分
watch也可以用来查看文件变化的情况，例如：
例如 watch ls -la file，这条命令的意思是没两秒察看 file1的文件大小变化情况。
退出： ctrl+c
watch命令详解
NAME
watch - execute a program periodically, showing output fullscreen
SYNOPSIS
watch [-dhvt] [-n <seconds>] [--differences[=cumulative]] [--help] [--interval=<seconds>] [--no-title] [--version] <command>
DESCRIPTION
watch runs command repeatedly, displaying its output (the first screenfull). This allows you to watch the program output change over time. By default, the program is run every 2 seconds; use -n or --interval to specify a different interval.
The -d or --differences flag will highlight the differences between successive updates. The --cumulative option makes highlighting "sticky", presenting a running display of all positions that have ever changed. The -t or --no-title option turns off the header showing the interval, command, and current time at the top of the display, as well as the following blank line. watch will run until interrupted.
NOTE
Note that command is given to "sh -c" which means that you may need to use extra quoting to get the desired effect.
Note that 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.
EXAMPLES
To watch for mail, you might do: watch -n 60 from
To watch the contents of a directory change, you could use: watch -d ls -l
If youre only interested in files owned by user joe, you might use: watch -d 'ls -l | fgrep joe'
You can watch for your administrator to install the latest kernel with: watch uname -r (Just kidding.)呵呵
BUGS
Upon terminal resize, the screen will not be correctly repainted until the next scheduled update. All --differences highlighting is lost on that update as well.
Non-printing characters are stripped from program output. Use "cat -v" as part of the command pipeline if you want to see them.
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