perlreref - Perl Regular Expressions Reference

$var =~ /foo/;

$var !~ /foo/;

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 unless something indicates
          Unicode
    n  Non-capture mode. Don't let () fill in $1, $2, etc...

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

\       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 occurrences for the element preceding it
 [...]   Matches any one of the characters 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 previous group
 \g{name}     Named backreference
 \k<name>     Named backreference
 \k'name'     Named backreference
 (?P=name)    Named backreference (python syntax)

\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
\F  Foldcase until \E
\Q  Disable pattern metacharacters until \E
\E  End modification

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

[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"

\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}';;
        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)
                   (Deprecated.)
   \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

           ASCII-         Full-
  POSIX    range          range    backslash
[[:...:]]  \p{...}        \p{...}   sequence    Description

-----------------------------------------------------------------------
alnum   PosixAlnum       XPosixAlnum            Alpha plus Digit
alpha   PosixAlpha       XPosixAlpha            Alphabetic characters
ascii   ASCII                                   Any ASCII character
blank   PosixBlank       XPosixBlank   \h       Horizontal whitespace;
                                                  full-range also
                                                  written as
                                                  \p{HorizSpace} (GNU
                                                  extension)
cntrl   PosixCntrl       XPosixCntrl            Control characters
digit   PosixDigit       XPosixDigit   \d       Decimal digits
graph   PosixGraph       XPosixGraph            Alnum plus Punct
lower   PosixLower       XPosixLower            Lowercase characters
print   PosixPrint       XPosixPrint            Graph plus Print, but
                                                  not any Cntrls
punct   PosixPunct       XPosixPunct            Punctuation and Symbols
                                                  in ASCII-range; just
                                                  punct outside it
space   PosixSpace       XPosixSpace            [\s\cK]
                 PerlSpace        XPerlSpace    \s       Perl's whitespace def'n
 upper   PosixUpper       XPosixUpper            Uppercase characters
 word    PosixWord        XPosixWord    \w       Alnum + Unicode marks +
                                                  connectors, like '_'
                                                  (Perl extension)
xdigit  ASCII_Hex_Digit  XPosixDigit            Hexadecimal digit,
                                                   ASCII-range is
                                                   [0-9A-Fa-f]

  POSIX      traditional   Unicode
[:digit:]       \d        \p{Digit}
[:^digit:]      \D        \P{Digit}

^  Match string start (or line, if /m is used)
   $  Match string end (or line, if /m is used) or before newline
\b{} Match boundary of type specified within the braces
\B{} Match wherever \b{} doesn't match
\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 $&

Maximal Minimal Possessive Allowed range
------- ------- ---------- -------------
{n,m}   {n,m}?  {n,m}+     Must occur at least n times
                           but no more than m times
{n,}    {n,}?   {n,}+      Must occur at least n times
{n}     {n}?    {n}+       Must occur exactly n times
*       *?      *+         0 or more times (same as {0,})
+       +?      ++         1 or more times (same as {1,})
?       ??      ?+         0 or 1 time (same as {0,1})

(?#text)          A comment
   (?:...)           Groups subexpressions without capturing (cluster)
(?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
   (?=...)           Zero-width positive lookahead assertion
(?!...)           Zero-width negative lookahead assertion
   (?<=...)          Zero-width positive lookbehind assertion
(?<!...)          Zero-width negative lookbehind assertion
   (?>...)           Grab what we can, prohibit backtracking
(?|...)           Branch reset
   (?<name>...)      Named capture
(?'name'...)      Named capture
   (?P<name>...)     Named capture (python syntax)
(?[...])          Extended bracketed character class
   (?{ code })       Embedded code, return value becomes $^R
(??{ code })      Dynamic regex, return value used as regex
(?N)              Recurse into subpattern number N
   (?-N), (?+N)      Recurse into Nth previous/next subpattern
   (?R), (?0)        Recurse at the beginning of the whole pattern
   (?&name)          Recurse into a named subpattern
(?P>name)         Recurse into a named subpattern (python syntax)
   (?(cond)yes|no)
(?(cond)yes)      Conditional expression, where "cond" can be:
                                       (?=pat)   look-ahead
                  (?!pat)   negative look-ahead
                                       (?<=pat)  look-behind
                  (?<!pat)  negative look-behind
                                       (N)       subpattern N has matched something
                                       (<name>)  named subpattern has matched something
                                       ('name')  named subpattern has matched something
                                       (?{code}) code condition
                  (R)       true if recursing
                  (RN)      true if recursing into Nth subpattern
                  (R&name)  true if recursing into named subpattern
                  (DEFINE)  always false, no no-pattern allowed

$_    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

$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

lc          Lowercase a string
lcfirst     Lowercase first char of a string
uc          Uppercase a string
ucfirst     Titlecase first char of a string
fc          Foldcase a string

pos         Return or set current match position
quotemeta   Quote metacharacters
reset       Reset ?pattern? status
study       Analyze string for optimizing matching

split       Use a regex to split a string into parts