Sed and remove string between two patterns

regular expressionsed

I've got problem with removing part of string between two patterns with sed. I've always got last PATTERN-2 in line:

test.txt:

PATTERN-1xxxxPATTERN-2aaa
PATTERN-1xxxxPATTERN-2fffPATTERN-1zzzzPATTERN-2gggPATTERN-1zzzzPATTERN-2
PATTERN-1xxxxPATTERN-2bbb

cmd

sed 's/PATTERN-1.*PATTERN-2//g' test.txt

the result of above is

aaa

bbb

but I would like to have

aaa
fffggg
bbb

Is possible to find PATTERN-2 which is closest to PATTERN-1?

Best Answer

As @steeldriver points out, it is easy if you have non-greedy regexps. If not, you can do it with a loop, like this:

sed ':a;s/PATTERN-2/\n/;s/PATTERN-1.*\n//;ta' test.txt

This works because we know there are no newlines in the middle of any line. It would also work with any other character that does not occur in any line, e.g. §.

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SED and GREP – Get All Regex Matches Between Two Patterns

IF GNU grep is an option, you could pass the -P (perl-compatible regex) flag and use lookahead assertions, lookbehind assertions and non-greedy matches to pull out what you need

echo 'xxSTART relevanttext xxEND something else xxSTART even more relevant'  |\
grep -oP '(?<=START).*?(?=xxEND|$)'
relevanttext
even more relevant

Or as Stephane Chazelas suggests, use the nifty \K in place of the look-behind assertion

echo 'xxSTART relevanttext xxEND something else xxSTART even more relevant'  |\
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sed 's/\((TAB)\)\{2,8\}/(TAB)/g'

Best Answer

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SED and GREP – Get All Regex Matches Between Two Patterns

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