Regular Expressions 101

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/
^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$
/
mi
^ asserts position at start of a line
1st Capturing Group
([a-z0-9_\.-]+)
Match a single character present in the list below
[a-z0-9_\.-]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
a-z matches a single character in the range between a (index 97) and z (index 122) (case insensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case insensitive)
_ matches the character _ with index 9510 (5F16 or 1378) literally (case insensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case insensitive)
- matches the character - with index 4510 (2D16 or 558) literally (case insensitive)
This hyphen is treated literally, which might be confusing for others. Consider escaping it or placing at the start or end of the class!
@ matches the character @ with index 6410 (4016 or 1008) literally (case insensitive)
2nd Capturing Group
([\da-z\.-]+)
Match a single character present in the list below
[\da-z\.-]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\d matches a digit (equivalent to [0-9])
a-z matches a single character in the range between a (index 97) and z (index 122) (case insensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case insensitive)
- matches the character - with index 4510 (2D16 or 558) literally (case insensitive)
This hyphen is treated literally, which might be confusing for others. Consider escaping it or placing at the start or end of the class!
\. matches the character . with index 4610 (2E16 or 568) literally (case insensitive)
3rd Capturing Group
([a-z\.]{2,6})
Match a single character present in the list below
[a-z\.]
{2,6} matches the previous token between 2 and 6 times, as many times as possible, giving back as needed (greedy)
a-z matches a single character in the range between a (index 97) and z (index 122) (case insensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case insensitive)
$ asserts position at the end of a line
Global pattern flags
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/
mi

Test String