yegor256 yegor256 - 3 years ago 96
Linux Question

What's wrong with my lookahead regex in GNU sed?

This is what I'm doing (simplified example):

gsed -i -E 's/^(?!foo)(.*)$/bar\1/' file.txt


I'm trying to put
bar
in front of every line that doesn't start with
foo
. This is the error:

gsed: -e expression #1, char 22: Invalid preceding regular expression


What's wrong?

Answer Source

As far as I know sed has not neither look-ahead nor look-behind. Switch to a more powerful language with similar syntax, like perl.

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