Regex cheatsheet

regex.txt

regex characters:
  .
    any character except newline
  [ ]
    any single character of set
  [^ ]
    any single character NOT of set
  *
    0 or more previous regular expression
  *?
    0 or more previous regular expression (non-greedy)
  +
    1 or more previous regular expression
  +?
    1 or more previous regular expression (non-greedy)
  ?
    0 or 1 previous regular expression
  |
    alternation
  ( )
    grouping regular expressions
  ^
    beginning of a line or string
  $
    end of a line or string
  {m,n}
    at least m but most n previous regular expression
  {m,n}?
    at least m but most n previous regular expression (non-greedy)
  \1-9
    nth previous captured group
  \&
    whole match
  \`
    pre-match
  \'
    post-match
  \+
    highest group matched
  \A
    beginning of a string
  \b
    backspace(0x08)(inside[]only)
  \b
    word boundary(outside[]only)
  \B
    non-word boundary
  \d
    digit, same as[0-9]
  \D
    non-digit
  \S
    non-whitespace character
  \s
    whitespace character[ \t\n\r\f]
  \W
    non-word character
  \w
    word character[0-9A-Za-z_]
  \z
    end of a string
  \Z
    end of a string, or before newline at the end
  (?#)
    comment
  (?:)
    grouping without backreferences
  (?=)
    zero-width positive look-ahead assertion
  (?!)
    zero-width negative look-ahead assertion
  (?>)
    nested anchored sub-regexp. stops backtracking.
  (?imx-imx)
    turns on/off imx options for rest of regexp.
  (?imx-imx:re)
    turns on/off imx options, localized in group.

special character classes:
  [:alnum:]
    alpha-numeric characters
  [:alpha:]
    alphabetic characters
  [:blank:]
    whitespace - does not include tabs, carriage returns, etc
  [:cntrl:]
    control characters
  [:digit:]
    decimal digits
  [:graph:]
    graph characters
  [:lower:]
    lower case characters
  [:print:]
    printable characters
  [:punct:]
    punctuation characters
  [:space:]
    whitespace, including tabs, carriage returns, etc
  [:upper:]
    upper case characters
  [:xdigit:]
    hexadecimal digits

options:
  /i
    case insensitive
  /o
    only interpolate #{} blocks once
  /m
    multiline mode - '.' will match newline
  /x
    extended mode - whitespace is ignored
  /[neus]
    encoding: none, EUC, UTF-8, SJIS, respectively