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

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"(S[0-9]+-[0-9]+-[0-9]+|S[0-9]+)" test_str = ("Samples\n" "101003 W1D1 Pre\n" "101003 W1D1 4H\n" "101003 W1D2 Pre\n" "101003 W2D1 Pre\n" "101004 W1D1 Pre\n" "101004 W1D1 4H\n" "101004 W1D2 Pre\n" "101004 W2D1 Pre\n" "101005 W1D1 Pre\n" "101005 W1D1 4H\n" "101005 W1D2 Pre\n" "101005 W2D1 Pre\n" "101007 W1D1 Pre\n" "101007 W1D1 4H\n" "101007 W1D2 Pre\n" "101007 W2D1 Pre\n" "102001 W1D1 Pre\n" "102001 W1D1 4H\n" "102001 W1D2 Pre\n" "102001 W2D1 Pre\n" "102002 W1D1 Pre\n" "102002 W1D1 4H\n" "102002 W1D2 Pre\n" "102002 W2D1 Pre\n" "102005 W1D1 Pre\n" "102005 W1D1 4H\n" "102005 W1D2 Pre\n" "102005 W2D1 Pre\n" "104001 W1D1 Pre\n" "104001 W1D1 4H\n" "104001 W1D2 Pre\n" "104001 W2D1 Pre\n" "104002 W1D1 Pre\n" "104002 W1D1 4H\n" "104002 W1D2 Pre\n" "104002 W2D1 Pre\n" "104005 W1D1 Pre\n" "104005 W1D1 4H\n" "104005 W1D2 Pre\n" "104005 W2D1 Pre\n" "105001 W1D1 Pre\n" "105001 W1D1 4H\n" "105001 W1D2 Pre\n" "105001 W2D1 Pre\n" "105002 W1D1 Pre\n" "105002 W1D1 4H\n" "105002 W1D2 Pre\n" "105002 W2D1 Pre\n" "105005 W1D1 Pre\n" "105005 W1D1 4H\n" "105005 W1D2 Pre\n" "105005 W2D1 Pre\n") matches = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # 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