How to highlight keywords when using tail

October 16th, 2012

Warning: This post is 12 years old. Some of this information may be out of date.

Have you ever been tailing a log file looking for a specific keyword or phrase? Maybe you're tailing an Exim log watching for an email, or an Apache log file for a specific request. Wouldn't it be really great if you could highlight the keyword or phrase?

Here's How to highlight keywords when using tail.

tail -f file.log | perl -pe 's/keyword/\e[1;31;43m$&\e[0m/g'

The "\e.../g" section can be replaced by some semicolon-separated integers, with the meaning:

0 : all attributes off
1 : bold
31 : foreground red
43 : background yellow

"keyword", of course, can be any perl regular expression:

(foo|bar) highlight the strings foo and bar
\b((foo|bar)\b highlight the words foo and bar
._\b((foo|bar)\b._ highlight the whole line that contains the words foo or bar