Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
gmx

Test String

Code Generator

Language

Generated Code

$re = '/(?<!\\\\) # negative look-behind to make sure start is not escaped (?: # start non-capture group for all possible match starts # group 1, match dollar signs only # single or double dollar sign enforced by look-arounds ((?<!\$)\${1,2}(?!\$))| # group 2, match escaped parenthesis (\\\\\()| # group 3, match escaped bracket (\\\\\[)| # group 4, match begin equation (\\\\begin\{equation\}) ) # if group 1 was start (?(1) # non greedy match everything in between # group 1 matches do not support recursion (.*?)(?<!\\\\) # match ending double or single dollar signs (?<!\$)\1(?!\$)| # else (?: # greedily and recursively match everything in between # groups 2, 3 and 4 support recursion (.*(?R)?.*)(?<!\\\\) (?: # if group 2 was start, escaped parenthesis is end (?(2)\\\\\)| # if group 3 was start, escaped bracket is end (?(3)\\\\\]| # else group 4 was start, match end equation \\\\end\{equation\} ) ))))/mx'; $str = 'NOTE: For test purposes each test has been contained to one line, please enable the s flag for multi-line matches. $ match $ don\'t match nested $ match $ $$ no match$ $no match$$ \\\\$no match\\\\$ $no match\\\\$ \\\\$no match\\\\$ $$ match $$ don\'t match nested $$ match $$ $$$ no match $$ $$ no match $$$ \\\\$$ no match$$ $$ no match\\\\$$ \\\\$$ no match\\\\$$ \\( match \\) \\( 1 \\( nested match \\) 3 \\) \\\\( no match \\\\) \\( no match \\\\\\\\) \\\\\\\\( no match \\\\\\\\) \\[ match \\] \\[ 1 \\[ nested match \\] 3 \\] \\\\\\\\[ no match \\\\] \\\\[ no match \\\\\\\\] \\\\\\\\[ no match \\\\\\\\] \\begin{equation} match \\end{equation} \\begin{equation} 1 \\begin{equation} nested match \\end{equation} \\end{equation} \\\\\\\\begin{equation} no match \\\\end{equation} \\\\begin{equation} no match \\\\\\\\end{equation} \\\\\\\\begin{equation} no match \\\\end{equation}'; preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0); // Print the entire match result var_dump($matches);

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php