Perl: Compact Regular Expressions (RegExp) Reference.

Quick reference to Perl’s regular expressions.

OPERATOR
=~ determines to which variable the regex is applied. In its absence, $_ is used.

$var =~ /foo/;

!~ determines to which variable the regex is applied, and negates the result of the match; it returns false if the match succeeds, and true if it fails.

$var !~ /foo/;

m/pattern/msixpogcdual searches a string for a pattern match, applying the given options.

m Multiline mode - ^ and $ match internal lines
s match as a Single line - . matches \n
i case-Insensitive
x eXtended legibility - free whitespace and comments
p Preserve a copy of the matched string -
${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be defined.
o compile pattern Once
g Global - all occurrences
c don't reset pos on failed matches when using /g
a restrict \d, \s, \w and [:posix:] to match ASCII only
aa (two a's) also /i matches exclude ASCII/non-ASCII
l match according to current locale
u match according to Unicode rules
d match according to native rules unl. something indicates Unicode

If ‘pattern’ is an empty string, the last successfully matched regex is used.
Delimiters other than ‘/’ may be used for both this operator and the following ones.
The leading m can be omitted if the delimiter is ‘/’.

qr/pattern/msixpodual lets you store a regex in a variable, or pass one around.
Modifiers as for m//, and are stored within the regex.

s/pattern/replacement/msixpogcedual substitutes matches of ‘pattern’ with ‘replacement’.
Modifiers as for m//, with two additions:

e Evaluate 'replacement' as an expression
r Return substitution and leave the original string untouched.

‘e’ may be specified multiple times.
‘replacement’ is interpreted as a double quoted string unless a single-quote (‘) is the delimiter.
?pattern? is like m/pattern/ but matches only once.
No alternate delimiters can be used. Must be reset with reset().

SYNTAX

\ Escapes the character immediately following it
. Matches any single character except a newline (unless /s is used)
^ Matches at the beginning of the string (or line, if /m is used)
$ Matches at the end of the string (or line, if /m is used)
* Matches the preceding element 0 or more times
+ Matches the preceding element 1 or more times
? Matches the preceding element 0 or 1 times
{...} Specifies a range of occurr. for the element preceding it
[...] Matches any one of the chars contained within the brackets
(...) Groups subexpressions for capturing to $1, $2...
(?:...) Groups subexpressions without capturing (cluster)
| Matches either the subexpression preceding or following it
\g1 or \g{1}, \g2 ... Matches the text from the Nth group
\1, \2, \3 ... Matches the text from the Nth group
\g-1 or \g{-1}, \g-2 ... Matches the text from the Nth prev. group
\g{name} Named backreference
\k<name> Named backreference
\k'name' Named backreference
(?P=name) Named backreference (python syntax)

ESCAPE SEQUENCES
These work as in normal strings.

\a Alarm (beep)
\e Escape
\f Formfeed
\n Newline
\r Carriage return
\t Tab
\037 Char whose ordinal is the 3 octal digits, max \777
\o{2307} Char whose ordinal is the octal number, unrestricted
\x7f Char whose ordinal is the 2 hex digits, max \xFF
\x{263a} Char whose ordinal is the hex number, unrestricted
\cx Control-x
\N{name} A named Unicode character or character sequence
\N{U+263D} A Unicode character by hex ordinal
\l Lowercase next character
\u Titlecase next character
\L Lowercase until \E
\U Uppercase until \E
\Q Disable pattern metacharacters until \E
\E End modification

This one works differently from normal strings:

\b An assertion, not backspace, except in a character class

CHARACTER CLASSES

[amy] Match 'a', 'm' or 'y'
[f-j] Dash specifies "range"
[f-j-] Dash escaped or at start or end means 'dash'
[^f-j] Caret indicates "match any character _except_ these"

The following sequences (except \N ) work within or without a character class. The first six are locale aware, all are Unicode aware. See perllocale and perlunicode for details.

\d A digit
\D A nondigit
\w A word character
\W A non-word character
\s A whitespace character
\S A non-whitespace character
\h An horizontal whitespace
\H A non horizontal whitespace
\N A non newline (when not followed by '{NAME}'; experimental;
     not valid in a character class; equivalent to [^\n]; it's
     like '.' without /s modifier)
\v A vertical whitespace
\V A non vertical whitespace
\R A generic newline (?>\v|\x0D\x0A)
\C Match a byte (with Unicode, '.' matches a character)
\pP Match P-named (Unicode) property
\p{...} Match Unicode property with name longer than 1 character
\PP Match non-P
\P{...} Match lack of Unicode property with name longer than 1 char
\X Match Unicode extended grapheme cluster

ANCHORS
All are zero-width assertions.

^ Match string start (or line, if /m is used)
$ Match string end (or line, if /m is used) or before newline
\b Match word boundary (between \w and \W)
\B Match except at word boundary (between \w and \w or \W and \W)
\A Match string start (regardless of /m)
\Z Match string end (before optional newline)
\z Match absolute string end
\G Match where previous m//g left off
\K Keep the stuff left of the \K, don't include it in $&

VARIABLES

$_ Default variable for operators to use
$` Everything prior to matched string
$& Entire matched string
$' Everything after to matched string
${^PREMATCH} Everything prior to matched string
${^MATCH} Entire matched string
${^POSTMATCH} Everything after to matched string

The use of $` , $& or $’ will slow down all regex use within your program.
Starting with Perl 5.10, you can also use the equivalent variables ${^PREMATCH}, ${^MATCH} and ${^POSTMATCH} , but for them to be defined, you have to specify the /p (preserve) modifier on your regular expression.

$1, $2 ... hold the Xth captured expr
$+ Last parenthesized pattern match
$^N Holds the most recently closed capture
$^R Holds the result of the last (?{...}) expr
@- Offsets of starts of groups. $-[0] holds start of whole match
@+ Offsets of ends of groups. $+[0] holds end of whole match
%+ Named capture groups
%- Named capture groups, as array refs

Captured groups are numbered according to their opening parent.


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