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
/
(?<![^;])([^;]++;)(?=(?>[^;]*;)*?\1)
/
g
Negative Lookbehind
(?<![^;])
Assert that the Regex below does not match
Match a single character not present in the list below
[^;]
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
1st Capturing Group
([^;]++;)
Match a single character not present in the list below
[^;]
++ matches the previous token between one and unlimited times, as many times as possible, without giving back (possessive)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
Positive Lookahead
(?=(?>[^;]*;)*?\1)
Assert that the Regex below matches
Atomic Group
(?>[^;]*;)*?
Non-capturing group that discards backtracking positions once matched.
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
Match a single character not present in the list below
[^;]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
\1 matches the same text as most recently matched by the 1st capturing group
Global pattern flags
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
g

Test String

Substitution

Processing...