Regular Expressions 101

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  • PCRE2 (PHP >=7.3)
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/
([^rs])(?=\1+)|(rr)(?=r+)|(ss)(?=s+)
/
g
1st Alternative
([^rs])(?=\1+)
1st Capturing Group
([^rs])
Match a single character not present in the list below
[^rs]
rs matches a single character in the list rs (case sensitive)
Positive Lookahead
(?=\1+)
Assert that the Regex below matches
\1+
matches the same text as most recently matched by the 1st capturing group
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
2nd Alternative
(rr)(?=r+)
2nd Capturing Group
(rr)
rr matches the characters rr literally (case sensitive)
Positive Lookahead
(?=r+)
Assert that the Regex below matches
r+
matches the character r literally (case sensitive)
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
3rd Alternative
(ss)(?=s+)
3rd Capturing Group
(ss)
ss matches the characters ss literally (case sensitive)
Positive Lookahead
(?=s+)
Assert that the Regex below matches
s+
matches the character s literally (case sensitive)
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
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...