本文介绍了一款名为'watch'的实用Linux命令，它能够周期性地运行指定的程序并显示其输出，便于观察文件或目录的变化情况。默认情况下，程序每两秒运行一次，但可通过选项进行调整。此外，'watch'还支持突出显示连续更新之间的差异。
[url]http://beerpla.net/2007/08/04/watch-a-useful-linux-command-you-may-have-never-heard-of/[/url]
How many times did I want to watch a directory waiting for a file to appear in it? Constant ls, for example, quickly got boring. A quick Perl script that would reload ls every 5 seconds… yeah it works but it takes a while to type up, and often enough I'm too lazy for that. And then I found 'watch' – a utility that comes with most *nix distros. Look at this beauty [man watch]:
NAME
watch – execute a program periodically, showing output fullscreen
SYNOPSIS
DESCRIPTION
watch runs command repeatedly, displaying its output (the first screen
full). 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 you're only interested in files owned by user joe, you might use
watch -d 'ls -l | fgrep joe'
To see the effects of quoting, try these out
watch echo $$
watch echo '$$'
watch echo "'"'$$'"'"
You can watch for your administrator to install the latest kernel with
watch uname -r
(Just kidding.)
How many times did I want to watch a directory waiting for a file to appear in it? Constant ls, for example, quickly got boring. A quick Perl script that would reload ls every 5 seconds… yeah it works but it takes a while to type up, and often enough I'm too lazy for that. And then I found 'watch' – a utility that comes with most *nix distros. Look at this beauty [man watch]:
NAME
watch – execute a program periodically, showing output fullscreen
SYNOPSIS
watch [-dhvt] [-n ] [--differences[=cumulative]] [--help]
[--interval=] [--no-title] [--version]DESCRIPTION
watch runs command repeatedly, displaying its output (the first screen
full). This allows you to watch the program output change over time.
By default, the program is run every 2 seconds; use -n or –interval to
specify a different interval.
The -d or –differences flag will highlight the differences between
successive updates. The –cumulative option makes highlighting
"sticky", presenting a running display of all positions that have ever
changed. The -t or –no-title option turns off the header showing the
interval, command, and current time at the top of the display, as well
as the following blank line.
watch will run until interrupted.
NOTE
Note that command is given to "sh -c" which means that you may need to
use extra quoting to get the desired effect.
Note that POSIX option processing is used (i.e., option processing
stops at the first non-option argument). This means that flags after
command don't get interpreted by watch itself.
EXAMPLES
To watch for mail, you might do
watch -n 60 from
To watch the contents of a directory change, you could use
watch -d ls -l
If you're only interested in files owned by user joe, you might use
watch -d 'ls -l | fgrep joe'
To see the effects of quoting, try these out
watch echo $$
watch echo '$$'
watch echo "'"'$$'"'"
You can watch for your administrator to install the latest kernel with
watch uname -r
(Just kidding.)
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