Regular Expressions 101

Save & Share

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8
  • .NET 7.0 (C#)
  • Rust
  • Regex Flavor Guide

Function

  • Match
  • Substitution
  • List
  • Unit Tests

Tools

Sponsors
There are currently no sponsors. Become a sponsor today!
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

/
/
gm

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"^([ ]{6})(- )((?!name)\w+[:](?:[ ]*(?=\n\1[ ]{4}\S)|[ ]*\S.+))((?:\n\1[ ]{2}.+)*?)(?:\n(\1[ ]{2})(name[ ]*[:])((?:[ ]*(?![>|])\S.+\b)|(?:(?:[ ]*[>|])?\n\5[ ]+.+)*))[ ]*$" test_str = ("// YAML Textmate grammar name property hoister\n" "// Moves a later `name` key value pair in multi value block definition to the \n" "// top of its \n" "//\n" "// # Notes\n" "// - Indent size is assumed to be 2.\n" "// - Indent level of names being hoisted is controlled by capture group $1,\n" "// which is later referenced by $5, the indent level of all other properties\n" "// - Other properties can be hoisted by replacing the two instances of `name`\n" "// in the pattern. A couple inputs for simple nested, folded, and literal values \n" "// (immediately after these notes) seem to work.\n" "// - Syntax level comments in captures will probably need to be rearranged after \n" "// applying this, and worst case (especially comments lower indents) break matching\n\n" " - match: '\\s*(\\,)\\s*'\n" " name:\n" " 'Testing': Regex101.Debug.Nested.Name\n" " - match: '\\s*(\\,)\\s*'\n" " name:\n" " 'Testing': Regex101.Debug.Nested.Name.TrailingWhitespace \n" " - match: '\\s*(\\,)\\s*'\n" " # Comment\n" " name:\n" " 'Testing': Regex101.Debug.Nested.Name.TrailingWhitespace \n" " - match: '\\s*(\\,)\\s*'\n" " name: >\n" " Wow this is a long name?\n" " kind of sus\n" " - match: '\\s*(\\,)\\s*'\n" " name: |\n" " sus2\n" " - name: meta.selector.stylus\n" " match: '\\s*(\\,)\\s*'\n" " - match: \\*\n" " name: meta.selector.stylus \n" " - match: '\\s*(\\&)([a-zA-Z0-9_-]+)\\s*'\n" " captures:\n" " '2':\n" " name: entity.other.attribute-name.parent-selector-suffix.stylus\n" " name: meta.selector.stylus\n" " - match: \\s*(\\&)\\s*\n" " name: meta.selector.stylus\n" " - captures:\n" " '1':\n" " name: punctuation.definition.entity.css\n" " match: '(\\.)[a-zA-Z0-9_-]+'\n" " name: entity.other.attribute-name.class.css\n" " - captures:\n" " '1':\n" " name: punctuation.definition.entity.css\n" " match: '(#)[a-zA-Z][a-zA-Z0-9_-]*'\n" " name: entity.other.attribute-name.id.css\n" " - captures:\n" " '1':\n" " name: punctuation.definition.entity.css\n" " match: >-\n" " (:+)(after|before|content|first-letter|first-line|host|(-(moz|webkit|ms)-)?selection)\\b\n" " name: entity.other.attribute-name.pseudo-element.css\n" " - captures:\n" " '1':\n" " name: punctuation.definition.entity.css\n" " match: >-\n" " (:)((first|last)-child|(first|last|only)-of-type|empty|root|target|first|left|right)\\b\n" " name: entity.other.attribute-name.pseudo-class.css\n" " - captures:\n" " '1':\n" " name: punctuation.definition.entity.css\n" " match: >-\n" " (:)(checked|enabled|default|disabled|indeterminate|invalid|optional|required|valid)\\b\n" " name: entity.other.attribute-name.pseudo-class.ui-state.css\n" " - begin: '((:)not)(\\()'\n" " beginCaptures:\n" " '1':\n" " name: entity.other.attribute-name.pseudo-class.css\n" " '2':\n" " name: punctuation.definition.entity.css\n" " '3':\n" " name: punctuation.section.function.css\n" " end: \\)\n" " endCaptures:\n" " '0':\n" " name: punctuation.section.function.css\n" " patterns:\n" " - include: '#selector'\n" " - captures:\n" " '1':\n" " name: entity.other.attribute-name.pseudo-class.css\n" " '2':\n" " name: punctuation.definition.entity.css\n" " '3':\n" " name: punctuation.section.function.css\n" " '4':\n" " name: constant.numeric.css\n" " '5':\n" " name: punctuation.section.function.css\n" " match: >-\n" " ((:)nth-(?:(?:last-)?child|(?:last-)?of-type))(\\()(\\-?(?:\\d+n?|n)(?:\\+\\d+)?|even|odd)(\\))\n" " - match: '((:)dir)\\s*(?:(\\()(ltr|rtl)?(\\)))?'\n" " captures:\n" " '1':\n" " name: entity.other.attribute-name.pseudo-class.css\n" " '2':\n" " name: puncutation.definition.entity.css\n" " '3':\n" " name: punctuation.section.function.css\n" " '4':\n" " name: constant.language.css\n" " '5':\n" " name: punctuation.section.function.css\n" " - match: '((:)lang)\\s*(?:(\\()(\\w+(-\\w+)?)?(\\)))?'\n" " captures:\n" " '1':\n" " name: entity.other.attribute-name.pseudo-class.css\n" " '2':\n" " name: puncutation.definition.entity.css\n" " '3':\n" " name: punctuation.section.function.css\n" " '4':\n" " name: constant.language.css\n" " '6':\n" " name: punctuation.section.function.css\n" " - captures:\n" " '1':\n" " name: punctuation.definition.entity.css\n" " match: '(:)(active|hover|link|visited|focus)\\b'\n" " name: entity.other.attribute-name.pseudo-class.css\n" " - captures:\n" " '1':\n" " name: punctuation.definition.entity.css\n" " match: '(::)(shadow)\\b'\n" " name: entity.other.attribute-name.pseudo-class.css") subst = "$1$2$6$7\\n$5$3$4" # You can manually specify the number of replacements by changing the 4th argument result = re.sub(regex, subst, test_str, 0, re.MULTILINE) if result: print (result) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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 Python, please visit: https://docs.python.org/3/library/re.html