Regex (grep) Backward match

1
votes

I need a Regex which matches the closed [A-Za-z_0-9]*\.xml before ERROR.

The following input should match match_me.xml

  1. ERROR should be determined.
  2. The first [A-Za-z_0-9]*\.xml before ERROR should be matched. -> match_me.xml

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match_not_me.xml

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match_me.xml

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ERROR

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2
regexlinuxgrep

2 Answers

1
votes

You can use awk for this:

awk 'p && /ERROR/{print p; p==""} /^[A-Za-z_0-9]*\.xml$/{p=$0}' file

match_me.xml
  1. When a line matches our pattern we store that line in variable p
  2. When p is set and we encounter ERROR we print p and reset it to blank.
1
votes

grep (PCRE) solution:

grep -Poz 'ERROR[\s\S]+?\s\K[A-Za-z_0-9]+\.xml' <(tac file) && echo

  • tac file - concatenate lines of the file in reverse order

  • [\s\S]+? - matches any character in "non-greedy" manner

  • \K - ignoring previous match

The output:

match_me.xml