Translate regex between POSIX and PCRE
Convert character classes like [:alpha:] to PCRE shorthand \\w and back. Warnings flag PCRE features — named groups, lookarounds — that POSIX engines can't express.
- convert[:alpha:] → [A-Za-z]
- convert[:alnum:] → [A-Za-z0-9]
- infoPCRE adds \d \w \s shorthand, lookarounds, named groups, lazy quantifiers.
How to convert between POSIX and PCRE
Paste a regex in either flavour, pick the direction, and read the translated pattern alongside a list of conversions and warnings.
- 01
Pick a direction
Choose POSIX → PCRE or PCRE → POSIX. The shell switches placeholders and labels automatically.
Patterns are parsed with the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) work when the u flag is on.
patternECMAScriptliteralregexinput · literaldirection · regexPOSIX -> PCRE
loaded · ECMAScriptPCRE · ready - 02
Paste pattern
Drop your regex in. Character classes ([:alpha:]/\w), backslash anchors, and braces are examined.
Each flag character mirrors the ECMAScript literal: g enables iteration, i folds case, m anchors per line, s lets . match newlines, u unlocks proper Unicode, y is sticky, and d emits indices.
flagsoptionsg · i · mliveconfig · optionsregex · flags[[:digit:]]+
flags applied · liveECMA · live - 03
Read translation
Conversions list rewrites like [[:digit:]] → \d. Warnings call out named groups and lookarounds POSIX can't express.
Conversions translate flavour-specific constructs (lookarounds, named groups, character classes) — the converter flags anything that has no equivalent in the target engine.
convertflavourPCRE · RE2diffrun · outputdiff · converted\d+
matches · livediff · ready - 04
Copy result
Grab the converted pattern with one click and drop it into your grep / awk / sed / PCRE engine.
Copy writes via navigator.clipboard.writeText; downloads use a Blob and object URL, so nothing transits the network and the output is byte-identical to what you see on screen.
copyexportclipboardblobexport · exportedready · savedCopied
ready to shipsuccess
Regex patterns that don't melt down
Use named groups
(?<year>\d{4}) reads better than $1 and survives reordering. Supported in ECMAScript 2018+.
Anchor strictly
Use ^/$ with the m flag when matching whole lines. Without anchors, partial matches sneak through.
Avoid catastrophic backtracking
Nested quantifiers like (a+)+ can explode. Run patterns through ReDoS Detector first.
Escape every literal
Backslash any meta character you want literally: \.\$\^\*\+\?\(\)\[\]\{\}\|\\.
Test edge cases
Empty string, single character, unicode, the maximum length you expect — write fixtures for each.
Patterns aren’t parsers
Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.
When you need POSIX-aware translation
Bridging PCRE-rich regex with POSIX engines — grep, awk, sed, oldstyle Unix tools.
Port to grep / awk / sed
Lift a PCRE pattern down to ERE so basic Unix tools can use it. Compiles through the JavaScript RegExp constructor — engine quirks (Unicode property escapes, sticky matching, named groups) work when their flags are on. Error messages cite the exact position of any syntax issue.
ReDoS-safeOld shell scripts
Migrate POSIX patterns into modern PCRE-powered services. Pairs with the ReDoS detector to catch catastrophic backtracking before you deploy. A pattern that handles 1k-character input fine can become a denial-of-service vector on attacker-controlled 1M-character input.
ECMA-compliantBSD vs GNU tooling
Normalise patterns that need to run on both BSD and GNU coreutils. Output exports as JavaScript, Python re, Java util.regex, .NET System.Text.RegularExpressions, PCRE, and POSIX — language quirks are highlighted on conversion so you don't ship a JS-only pattern to a Go service.
spec-gradeDocument differences
Show colleagues which PCRE features POSIX engines refuse. Capture groups (named or numbered) round-trip cleanly into replacement strings, JSON output, or CSV extraction without re-typing. Backreferences ($1, ${name}) preserve semantics across languages.
cross-engineAudit class syntax
Catch [[:alpha:]] vs \w mismatches before deploying scripts. Test against edge cases — empty input, single character, max length, multibyte boundaries — to catch off-by-one and zero-length match bugs before they reach production.
test-readyCross-tool tests
Verify the same pattern behaves identically in grep -E and PCRE. All matching runs client-side so secret patterns never leave the browser. Useful when the pattern itself is sensitive (PII regexes, internal data formats, security filters).
production-readyFrequently asked questions
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