RegexQuill

Escape & unescape

Escape text for a regular expression

Turn any string into a pattern that matches it literally, in four regex flavours at once, ready to paste into code. Or go the other way.

Direction

JavaScript

PatternPrice: \$4\.99 \(sale\) \[\*today\*\] C:\\temp\\new\.txt\?
Regex literal/Price: \$4\.99 \(sale\) \[\*today\*\] C:\\temp\\new\.txt\?/
String for new RegExp()new RegExp("Price: \\$4\\.99 \\(sale\\) \\[\\*today\\*\\] C:\\\\temp\\\\new\\.txt\\?")

Escapes ^ $ \ . * + ? ( ) [ ] { } | and /, which is safe with and without the u and v flags.

Python re

PatternPrice:\ \$4\.99\ \(sale\)\ \[\*today\*\]\ C:\\temp\\new\.txt\?
Pythonre.compile(r"Price:\ \$4\.99\ \(sale\)\ \[\*today\*\]\ C:\\temp\\new\.txt\?")

Identical to re.escape() in Python 3.7 and later.

PCRE / PHP

PatternPrice\: \$4\.99 \(sale\) \[\*today\*\] C\:\\temp\\new\.txt\?
PHPpreg_match('/Price\: \$4\.99 \(sale\) \[\*today\*\] C\:\\\temp\\\new\.txt\?/', $subject)

Identical to PHP’s preg_quote() with the delimiter you choose.

POSIX ERE

PatternPrice: \$4\.99 \(sale\) \[\*today\*] C:\\temp\\new\.txt\?
Shellgrep -E 'Price: \$4\.99 \(sale\) \[\*today\*] C:\\temp\\new\.txt\?' file.txt

For grep -E, sed -E and awk. ] and } only need escaping inside a bracket expression.

Why each flavour escapes differently

A regex treats some characters as instructions: . means any character, * repeats, brackets and parentheses group. To match them literally, put a backslash in front. Which characters need it depends on the engine, and escaping too much can itself be an error.

  • JavaScript: escapes only the syntax characters and /. With the u or v flag an unnecessary escape such as \- or \# is a syntax error, so a minimal escape is the safe one. Line breaks are written as \n so the result also works inside a /literal/.
  • Python: the same set as re.escape(), which also escapes -, #, &, ~ and spaces, because they matter in verbose mode and inside classes.
  • PCRE / PHP: the same as preg_quote(), plus the delimiter you wrap the pattern in.
  • POSIX ERE: for grep -E, sed -E and awk. The shell form wraps the pattern in single quotes so the shell leaves it alone.

Unescape works the other way: paste an escaped pattern and get the literal text back. If the pattern contains real regex syntax, such as an unescaped dot or a \d, the tool points to the first one instead of guessing.

Questions

Does JavaScript have a built-in escape function?

Newer engines have RegExp.escape(), which also escapes a leading letter or digit and characters such as - and , as hex codes so the result is safe in more contexts. Its output is longer but matches the same text.

Can I use the escaped text inside [ ]?

These escapes are meant for use outside a character class. Inside one, only \, ], ^ and - are special, so escape those instead.

Is my text sent anywhere?

No. Escaping happens in your browser as you type.