Live match highlighting · group extraction · Python export
Pattern
Live
//g
Test String
0 chars · 0 lines
0 matches
Enter a pattern above to see matches.
Matches highlighted in test string
Replacement string — use $1, $2 for numbered groups · $<name> for named groups
Ready-to-run Python snippet using the re module
Bash snippets — grep / sed / awk
Export matched values
Run a match first, then export here.
Quick Patterns
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Cheat Sheet
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Build a regex and take it to your script
Type a pattern and test text to see every match highlighted, with capture groups listed and a replace preview. When it works, export it as Python or Bash so the pattern goes straight into a log-parsing script.
Common questions
Which regex flavour does this tester use?
Your browser’s JavaScript engine. Most everyday syntax is the same in Python, but some isn’t: named groups are written (?<name>…) here but (?P<name>…) in Python, and lookbehinds in Python must be fixed-width. grep and sed default to POSIX regex, where \d doesn’t exist; use [0-9] or grep -P.
How do I match an IP address with a regex?
\b(?:\d{1,3}\.){3}\d{1,3}\b finds anything that looks like an IPv4 address, which is usually enough for logs. It also accepts 999.1.1.1; to validate properly, check each number is 0–255 in code, for example with Python’s ipaddress module.
Why does my regex match too much?
.* is greedy and takes as much as it can, so ".*" spans from the first quote on a line to the last. Use the lazy .*?, or a negated class such as "[^"]*", which is faster and clearer.
How do I use a regex with grep?
grep -E 'pattern' file uses extended regex, and grep -oP 'pattern' file (GNU grep) uses Perl-style regex and prints only the matched part. Quote the pattern in single quotes so the shell doesn’t change it.
What do the flags g, i, m and s mean?
g finds all matches instead of the first, i ignores case, m makes ^ and $ match at each line, and s lets . match newlines. In Python these are re.I, re.M and re.S; “global” is re.findall or re.finditer.