Common Software

Watching commands and files

This tutorial should work properly on all Unix based OSes.


Watching commands:

If you need to keep an eye on a command whose output is changing, use the watch

For example, to keep an eye on your load average:


$ watch ‘cat /proc/loadavg’


Every two seconds, watch runs the cat command again. Use Ctrl+c to quit. To
change the refresh rate to 10 seconds, type the following:


$ watch -n 10 ‘ls -l’


To highlight the difference between screen updates, type:


$ watch -d ‘ls -l’


Type Ctrl+c to exit the watch command.


Watching Files:

You can use the watch command to watch the size of a file. For example, to watch a large ISO file named mydownload.iso as it downloads, use the following command:


$ watch ‘ls –l mydownload.iso’


To watch the contents of a plain text file grow over time, you can use the tail com-
mand. For example, you can watch as messages are added to the /var/log/messages
file as follows:


$ tail -f /var/log/messages


Pressing Ctrl+c will exit from the tail command.

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