Regular Expressions 101

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/
\b([^;]+)(?!.*\1);
/
g
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
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, giving back as needed (greedy)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
Negative Lookahead
(?!.*\1)
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)
\1 matches the same text as most recently matched by the 1st capturing group
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
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