Quick tip: Easily find strings with grep color highlighting feature

Posted on in Categories Linux, Shell scripting, Sys admin, Tips, UNIX last updated October 11, 2007

grep command is the de facto tool for searching text files. However when there are too many matches, it can be difficult to find the requested text in the search results. grep comes with –color=’auto’ option. It surrounds the matching string with the colour, thus resulting enhanced output.

Finding string with color highlighting

Pass –color option to grep command:
# grep --color='auto' -i error /var/log/messages

Oct  9 16:12:14 vivek-desktop kernel: [   11.555442] bt878: probe of 0000:05:00.1 failed with error -22
Oct 10 17:35:28 vivek-desktop kernel: [   10.564710] bt878: probe of 0000:05:00.1 failed with error -22
Oct 11 10:15:34 vivek-desktop kernel: [   12.187477] bt878: probe of 0000:05:00.1 failed with error -22
Oct 11 14:29:56 vivek-desktop kernel: [   11.135309] bt878: probe of 0000:05:00.1 failed with error -22

Now all matched text displayed using red color. The –color option to matches in the input in red color by default. Color is added via ANSI escape sequences. To change color use environment variable GREP_COLOR. Following will set background to red and foreground to white:
$ export GREP_COLOR='1;37;41'
$ egrep --color=auto -i '(error|fatal|warn|drop)' /var/log/messages

Quick tip: Easily find strings with gep color highlighting feature
I recommend putting following in ~/.bash_profile OR ~/.bashrc file:
$ vi ~/.bash_profile
Append following alias:
export GREP_COLOR='1;37;41'
alias grep='grep --color=auto'

Save and close the file. Please note that –color option works with many GNU text utilities, so feel free to use the same.

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

6 comment

  1. Unfortunately when I pipe the output through ‘more’ it strips out the color. Not even using ‘more -R’ or ‘more -r’ will work. Color output from ‘ls’ does not get stripped, but color output from grep does get stripped out when piped through ‘more’ (or ‘less’). OS: MAC-OSX 10.6.

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