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

Question

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 1

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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