Regular Expressions 101

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/
\s*[()](?=(?:[^@]*@[^@]*@)*[^@]*$)\s*
/
gm
\s
matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Match a single character present in the list below
[()]
()
matches a single character in the list () (case sensitive)
Positive Lookahead
(?=(?:[^@]*@[^@]*@)*[^@]*$)
Assert that the Regex below matches
Non-capturing group
(?:[^@]*@[^@]*@)*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
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 6410 (4016 or 1008) literally (case sensitive)
@ matches the character @ with index 6410 (4016 or 1008) literally (case sensitive)
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 6410 (4016 or 1008) literally (case sensitive)
@ matches the character @ with index 6410 (4016 or 1008) literally (case sensitive)
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 6410 (4016 or 1008) literally (case sensitive)
$ asserts position at the end of a line
\s
matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
* matches the previous token between zero 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)
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.

Regular Expression
No Match

/
/
gm

Test String

Substitution

Processing...