Regular Expressions 101

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/
^[^\W@]+@[^\.]+\..+$
/
gm
^ asserts position at start of a line
Match a single character not present in the list below
[^\W@]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\W matches any non-word character (equivalent to [^a-zA-Z0-9_])
@ 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 one and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
.
matches any character (except for line terminators)
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of a line
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