Regular Expressions 101

Save & Share

  • Save Regex
    ctrl+s
  • Update Regex
    ctrl+⇧+s

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8

Function

  • Match
  • Substitution
  • List
  • Unit Tests
/
^((?:::|[^:])*+):(?!.*(?<!:):(?!:))
/
gm
^ asserts position at start of a line
1st Capturing Group
((?:::|[^:])*+)
Non-capturing group
(?:::|[^:])*+
*+ matches the previous token between zero and unlimited times, as many times as possible, without giving back (possessive)
1st Alternative
::
::
matches the characters :: literally (case sensitive)
2nd Alternative
[^:]
Match a single character not present in the list below
[^:]
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
Negative Lookahead
(?!.*(?<!:):(?!:))
Assert that the Regex below does not match
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Negative Lookbehind
(?<!:)
Assert that the Regex below does not match
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
Negative Lookahead
(?!:)
Assert that the Regex below does not match
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gm

Test String