Regex cheatsheet

Many programs use regular expression to find & replace text. However, they tend to come with their own different flavor.

You can probably expect most modern software and programming languages to be using some variation of the Perl flavor, "PCRE"; however command-line tools (grep, less, ...) will often use the POSIX flavor (sometimes with an extended variant, e.g. egrep or sed -r). ViM also comes with its own syntax (a superset of what Vi accepts).

This cheatsheet lists the respective syntax of each flavor, and the software that uses it.

If you spot errors or missing data, or just want to make this prettier/more accurate, don't hesitate to open an issue or a pull request.

Syntax

WhatPerl/PCREPython's rePOSIX (BRE)POSIX extended (ERE)ViM
Basics
Custom character class[...][...][...][...][...]
Negated custom character class[^...][^...][^...][^...][^...]
\ special in class?yesyesno, ] escaped if comes first
Ranges[a-z], - escaped if comes last[a-z], - escaped if first or last[a-z], - escaped if comes last[a-z]
Alternation||\||\| \& (low precedence)
Escaped character\033 \x1B \x{1234} \N{name} \N{U+263D}\x12\%d123 \%x2A \%u1234 \%U1234ABCD
Character classes
Any character (except newline).....
Any character (including newline)\_.
Match a "word" character (alphanumeric plus _)\w [[:word:]]\w\w\w\w
Case[[:upper:]] / [[:lower:]][[:upper:]] / [[:lower:]][[:upper:]] / [[:lower:]]\u [[:upper:]] / \l [[:lower:]]
Match a non-"word" character\W\W\W
Match a whitespace character (except newline)\s [[:space:]]\s [[:space:]]\s [[:space:]]
Whitespace including newline\s [[:space:]]\s\_s
Match a non-whitespace character\S\S[^[:space:]][^[:space:]]\S [^[:space:]]
Match a digit character\d [[:digit:]]\d[[:digit:]][[:digit:]]\d [[:digit:]]
Match a non-digit character\D\D[^[:digit:]][^[:digit:]]\D [^[:digit:]]
Any hexadecimal digit[[:xdigit:]][[:xdigit:]][[:xdigit:]]\x [[:xdigit:]]
Any octal digit\o
Any graphical character excluding "word" characters[[:punct:]][[:punct:]][[:punct:]][[:punct:]]
Any alphabetical character[[:alpha:]][[:alpha:]][[:alpha:]]\a [[:alpha:]]
Non-alphabetical character[^[:alpha:]][^[:alpha:]]\A [^[:alpha:]]
Any alphanumerical character[[:alnum:]][[:alnum:]][[:alnum:]][[:alnum:]]
ASCII[[:ascii:]]
Character equivalents (e = é = è) (as per locale)[[=e=]][[=e=]][[=e=]]
Zero-width assertions
Word boundary\b\b\b\b\< / \>
Anywhere but word boundary\B\B\B\B
Beginning of line/string^ / \A^ / \A^^^ (beginning of pattern ) \_^
End of line/string$ / \Z$ / \Z$$$ (end of pattern) \_$
Captures and groups
Capturing group(...) (?<name>...)(...) (?P<name>...)\(...\)(...)\(...\)
Non-capturing group(?:...)(?:...)\%(...\)
Backreference to a specific group.\1 \g1 \g{-1}\1\1\1 non-official\1
Named backreference\g{name} \k<name>(?P=name)
Look-around
Positive look-ahead(?=...)(?=...)\(...\)\@=
Negative look-ahead(?!...)(?!...)\(...\)\@!
Positive look-behind(?<=...)(?<=...)\(...\)\@<=
Negative look-behind(?<!...)(?<!...)\(...\)\@<!
Multiplicity
0 or 1??\??\?
0 or more*****
1 or more++\++\+
Specific number{n} {n,m} {n,}{n} {n,m} {n,}\{n\} \{n,m\} \{n,\}{n} {n,m} {n,}\{n} \{n,m} \{n,}
0 or 1, non-greedy?+??
0 or more, non-greedy*+*?\{-}
1 or more, non-greedy+++?
Specific number, non-greedy{n,m}+ {n,}+{n,m}? {n,}?\{-n,m} \{-n,}
0 or 1, don't give back on backtrack?+
0 or more, don't give back on backtrack*+
1 or more, don't give back on backtrack++
Specific number, don't give back on backtrack{n,m}+ {n,}?
Other
Independent non-backtracking pattern(?>...)\(...\)\@>
Make case-sensitive/insensitive(?i) / (?-i)(?i) / (?-i)\c / \C

Programs

WhatSyntaxComments/gotchas
Programming languages
PerlPCREPCRE is actually a separate implementation from Perl's, with slight differences
Python's re standard libPython's own syntax (Perl-inspired)
RubyRuby's own syntax (Perl-inspired)
Java's java.util.regexAlmost PCRE
Boost.RegexPCRE
Text editors
EclipsePCRE
Emacs?
NetbeansPCRE
Notepad++PCRE (Boost.Regex)
PyCharmPCREPerl-inspired
Sublime Text?
UltraEditPCRE
ViMViM
Command-line tools
awkEREmight depend on the implementation
grepBRE, egrep for ERE, grep -P for PCRE (optional)
lessEREusually; man page says "regular expression library supplied by your system"
screenplain text
sedBRE, -E switches to ERE