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Advanced sed find and replace

linux —

19 Jan 2010

I always forget how to do this, so, by god, I'm going to actually write it down this time so that I don't have to search all over the place next time.

To find a string of text and replace it with part of the original string intact:

sed -i 's/\(foo\)\([A-Z, -]*\)/\1\L\2/g' file.txt

Putting things in escaped parentheses creates a group—\(foo\) is group one, \([A-Z]*\) is group two. Then in the replace string, you call up a group by putting \#. So group 1 becomes \1. Thus, the above replacement string—\1\L\2—means keep group one as is but convert group two, whatever it might be, to lowercase.

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