Regular Expressions 101

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/
^([^@\.;]+@[^@\.;]+\.[^@\.;]+[;]*)*[^@.;]+$
/
^ asserts position at start of the string
1st Capturing Group
([^@\.;]+@[^@\.;]+\.[^@\.;]+[;]*)*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
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 6410 (4016 or 1008) literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
; matches the character ; with index 5910 (3B16 or 738) 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 one 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 4610 (2E16 or 568) literally (case sensitive)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
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 6410 (4016 or 1008) literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)
Match a single character 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)
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 a single character in the list @.; (case sensitive)
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/

Test String