In PCRE, POSIX character set names recognize only ASCII
characters. You can use ‘\Q...\E’ inside a character class.
Quantifiers
?
0 or 1, greedy
?+
0 or 1, possessive
??
0 or 1, lazy
*
0 or more, greedy
*+
0 or more, possessive
*?
0 or more, lazy
+
1 or more, greedy
++
1 or more, possessive
+?
1 or more, lazy
{n}
exactly n
{n,m}
at least n, no more than m, greedy
{n,m}+
at least n, no more than m, possessive
{n,m}?
at least n, no more than m, lazy
{n,}
n or more, greedy
{n,}+
n or more, possessive
{n,}?
n or more, lazy
Anchors and Simple Assertions
\b
word boundary
\B
not a word boundary
^
start of subject
also after internal newline in multiline mode
\A
start of subject
$
end of subject
also before newline at end of subject
also before internal newline in multiline mode
\Z
end of subject
also before newline at end of subject
\z
end of subject
\G
first matching position in subject
Match Point Reset
\K
reset start of match
Alternation
expr|expr|expr...
Capturing
(...)
capturing group
(?<name>...)
named capturing group (like Perl)
(?'name'...)
named capturing group (like Perl)
(?P<name>...)
named capturing group (like Python)
(?:...)
non-capturing group
(?|...)
non-capturing group; reset group numbers for
capturing groups in each alternative
Atomic Groups
(?>...)
atomic, non-capturing group
Comment
(?#....)
comment (not nestable)
Option Setting
(?i)
caseless
(?J)
allow duplicate names
(?m)
multiline
(?s)
single line (dotall)
(?U)
default ungreedy (lazy)
(?x)
extended (ignore white space)
(?-...)
unset option(s)
Lookahead and Lookbehind Assertions
(?=...)
positive look ahead
(?!...)
negative look ahead
(?<=...)
positive look behind
(?<!...)
negative look behind
Each top-level branch of a look behind must be of a fixed length.
Backreferences
\n
reference by number (can be ambiguous)
\gn
reference by number
\g{n}
reference by number
\g{-n}
relative reference by number
\k<name>
reference by name (like Perl)
\k'name'
reference by name (like Perl)
\g{name}
reference by name (like Perl)
\k{name}
reference by name (like .NET)
(?P=name)
reference by name (like Python)
Subroutine References (possibly recursive)
(?R)
recurse whole pattern
(?n)
call subpattern by absolute number
(?+n)
call subpattern by relative number
(?-n)
call subpattern by relative number
(?&name)
call subpattern by name (like Perl)
(?P>name)
call subpattern by name (like Python)
Conditional Patterns
(?(condition)yes-pattern)
(?(condition)yes-pattern|no-pattern)
(?(n)...
absolute reference condition
(?(+n)...
relative reference condition
(?(-n)...
relative reference condition
(?(<name>)...
named reference condition (like Perl)
(?('name')...
named reference condition (like Perl)
(?(name)...
named reference condition (PCRE only)
(?(R)...
overall recursion condition
(?(Rn)...
specific group recursion condition
(?(R&name)...
specific recursion condition
(?(DEFINE)...
define subpattern for reference
(?(assert)...
assertion condition
Backtracking Control
The following act immediately they are reached:
(*ACCEPT)
force successful match
(*FAIL)
force backtrack; synonym ‘(*F)’
The following act only when a subsequent match failure causes a backtrack to
reach them. They all force a match failure, but they differ in what happens
afterwards. Those that advance the start-of-match point do so only if the
pattern is not anchored.
(*COMMIT)
overall failure, no advance of starting point
(*PRUNE)
advance to next starting character
(*SKIP)
advance start to current matching position
(*THEN)
local failure, backtrack to next alternation
Newline Conventions
These are recognized only at the very start of the pattern or after a
‘(*BSR_...)’ option.
(*CR)
(*LF)
(*CRLF)
(*ANYCRLF)
(*ANY)
What ‘\R’ Matches
These are recognized only at the very start of the pattern or after a
‘(*...)’ option that sets the newline convention.