watch (Unix)

watch is a GNU command-line tool that runs the specified command repeatedly and displays the output on stdout so you can watch it change over time. By default, the command is run every 2 seconds, although this is adjustable with the -n secs argument. Since the command is passed to sh -c, you may need to encase it in quotes for it to run correctly.

Syntax

watch [options] command [command options]

Example

watch "ps aux | grep php"

This will generate a list of processes every 2 seconds, filter for all lines that contain the word "php", and display the results on the screen. The output might look something like this:

Every 2s: ps aux | grep php                             Tue Jan 30 14:56:33 2007

reconst  30028  0.0  0.0  7044 2596 ?        S    Jan23   0:00 vim -r core/html_api.php
cinonet  28009  0.0  0.2 20708 11064 ?       SN   Jan25   0:30 php5.cgi
donoiz   23810  0.0  0.2 22740 10996 ?       SN   Jan27   0:30 php.cgi 43/pdf

The watch command is useful for viewing changes over time, like repeatedly running the ls -l command to watch a file's size change, or running ps as in the above example to monitor certain processes continuously.

Arguments

• -d – Highlights differences between iterations
• -h – Displays a help message, then exits
• -n secs – Specifies the interval between executions of the command in seconds
• -t – Tells watch not to display the header
• -v – Prints version information, then exits

See also

List of Unix commands

External links

• watch(1): execute a program periodically, showing output fullscreen – Linux User Commands Manual