Reference – What does this regex mean?

by

The Stack Overflow Regular Expressions FAQ

See also a lot of general hints and useful links at the regex tag details page.

Online tutorials

Quantifiers

Character Classes

Escape Sequences

Anchors

anchor matches flavors
^ Start of string Common*
^ Start of line Commonm
$ End of line Commonm
$ End of text Common*
$ The very end of string phpD, javascript
\A Start of string Common except js
\Z End of text Common except js python
\Z The very end of string python
\z The very end of string Common except js python
\b Word boundary Common
\B Not a word boundary Common
\G End of previous match Common except js, python re
Term Definition
Start of string At the very start of the string.
Start of line At the very start of the string, and
after a non-terminal line terminator.
End of string At the very end of the string.
End of text At the very end of the string, and
at a terminal line terminator.
End of line At the very end of the string, and
at a line terminator.
Word boundary At a word character not preceded by a word character, and
at a non-word character not preceded by a non-word character.
End of previous match At a previously set position, usually where a previous match ended.
At the very start of the string if no position was set.

“Common” refers to the following: icu java js .net objective-c pcre perl php python swift ruby

* Default |
m Multi-line mode. |
D Dollar end only mode.

Groups

Lookarounds

Modifiers

flag modifier flavors
a ASCII python
c current position perl
e expression php perl
g global most
i case-insensitive most
m multiline php perl python javascript .net java
m (non)multiline ruby
o once perl ruby
S study php
s single line ruby
U ungreedy php r
u unicode most
x whitespace-extended most
y sticky ↪ javascript

Other:

Common Tasks

Advanced Regex-Fu

Flavor-Specific Information

(Except for those marked with *, this section contains non-Stack Overflow links.)

General information

(Links marked with * are non-Stack Overflow links.)

Examples of regex that can cause regex engine to fail

Tools: Testers and Explainers

(This section contains non-Stack Overflow links.)

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