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

/
/
gm

Test String

Code Generator

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "^ *[^\\s]+( +[^\\s]+)*$"; final String string = "# UFIS : User-Friendly and Instant Installer System\n\n" + "# Each comment starts with '#' and ends with a new line.\n" + "# Each statement is written in one line.\n" + "# Commands' and built-in variables' names are always uppercase.\n" + "# A custom variable name must have at least one lowercase character and must begin with a letter or the underscore (_).\n\n" + "LET APP_NAME = \"MyApp\"\n" + "LET APP_VERSION = \"1.0.0\"\n\n" + "LET a = MATERIAL \"folderx/\"\n" + "a -= \"test.exe\"\n" + "a -= \"main.exe\"\n" + "a += MATERIAL \"folderz/\"\n" + "a += MATERIAL \"README.md\"\n\n" + "LET b = MATERIAL \"folderx/test.exe\"\n\n" + "LET c = MATERIAL \"folderx/main.exe\"\n\n" + "IF INSTALLING\n" + " LET iAcceptLicense = INPUT CHECKBOX \"Accept [license](https://myapp.com/license)\" MANDATORY\n" + " IF iAcceptLicense == FALSE\n" + " QUIT\n" + " ENDIF\n\n" + " LET iLanguage = INPUT CHOICES \"Vietnamese\" OR \"English\" DEFAULT \"English\" MANDATORY\n\n" + " LET INSTALL_DIR = INPUT DIRECTORY \"Installation directory\" POSTFIX \"/${APP_NAME}\" DEFAULT PROGRAM_FILES\n" + " LET iInstallTest = INPUT CHECKBOX \"Install test.exe\" DEFAULT FALSE\n" + " LET iCreateDesktopShortcut = INPUT CHECKBOX \"Create desktop shortcut\" DEFAULT TRUE\n" + " LET iLaunchAtStartup = INPUT CHECKBOX \"Launch program at startup\" DEFAULT TRUE\n\n" + " INSTALL a AND c TO INSTALL_DIR # the same as \"${INSTALL_DIR}\"\n\n" + " IF iInstallTest == TRUE\n" + " INSTALL b TO INSTALL_DIR AS \"test_program.exe\"\n" + " ENDIF\n\n" + " IF iCreateDesktopShortcut == TRUE\n" + " CREATE SHORTCUT FOR c IN DESKTOP_ALL_USERS\n" + " ENDIF\n\n" + " IF iLaunchAtStartup == TRUE\n" + " RUN c AT STARTUP\n" + " ENDIF\n" + " \n" + " WORK registry_work\n" + " CREATE REGSZ \"HKEY_LOCAL_MACHINE/Software/${APP_NAME}\" VALUE \"1\"\n" + " ENDWORK\n" + " \n" + " CPP\n" + " #include <iostream>\n" + " \n" + " void entry() {\n" + " std::cout << \"Not very intelligent\";\n" + " }\n" + " ENDCPP\n" + " \n" + " CALL entry\n\n" + "ELIF RUNNING\n" + " RUN c\n\n" + "ELSE # UNINSTALLING\n" + " UNDO ALL EXCEPT registry_work\n\n" + "ENDIF\n"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); final Matcher matcher = pattern.matcher(string); while (matcher.find()) { System.out.println("Full match: " + matcher.group(0)); for (int i = 1; i <= matcher.groupCount(); i++) { System.out.println("Group " + i + ": " + matcher.group(i)); } } } }

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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html