Use of Linux watch command

1. Command Introduction

The watch command executes the given command in a periodic manner and displays the execution results on the full screen.

watch is a very useful command that comes with almost all Linux distributions. As the name suggests, watch can help monitor the running results of a command, saving us from running it manually over and over again. For example, tail a log file, ls monitors the size change of a file, etc. By default, the program runs every 2 seconds. You can use -n or --interval to specify the interval.

2. Command format

watch [OPTIONS] COMMAND

3. Option Description

-d, --differences [PERMANENT]
 Highlights the differences between the two most recent updates. -d cumulative option will highlight the changes (regardless of whether the most recent one has changed) -n, --interval SECONDS
 Specify the monitoring interval in seconds. The default value is 2s and cannot be lower than 0.1s
-p, --precise
 Try to monitor the command exactly at the specified interval -t, --no-title
 Turn off the output of the watch command at the top of the interval, command, and current time -b, --beep
 Beep when the exit code of the monitored command is non-zero -e, --errexit
 When an error occurs in the monitored command, watch stops updating and exits after pressing the key -g, --chgexit
 Exit watch when the monitored command output changes
-c, --color
 Interpret ANSI color and style sequences -x, --exec
 Pass the command to exec(2) instead of sh -c
-h, --help
 Display help information and exit -v, --version
 Display version information and exit

4. Common Examples

(1) Repeat the uptime command, by default it is executed every 2 seconds.

watch uptime

(2) Check the changes in the current directory file log.

watch -d "ls -l | grep log"

Note that when the monitored command contains a pipe, it needs to be enclosed in quotes.

(3) Check the average load of the system every 10 seconds.

watch -n10 cat /proc/loadavg

(4) Highlight the changes in the number of network connections every 1 second.

watch -n1 -d netstat -ant

References
[1] watch(1) manual

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