Regular Expressions 101

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/
^(?!.*\+\+) # não aceita dois "+" seguidos [_A-Za-z0-9-\+]+(\.[_A-Za-z0-9-]+)* # username @ # arroba [A-Za-z0-9-]+(\.[A-Za-z0-9]+)*(\.[A-Za-z]{2,})$ # domínio
/
gmx
^ asserts position at start of a line
Negative Lookahead
(?!.*\+\+)
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)
\+ matches the character + with index 4310 (2B16 or 538) literally (case sensitive)
\+ matches the character + with index 4310 (2B16 or 538) literally (case sensitive)
# não aceita dois "+" seguidos
não aceita dois "+" seguidos
Comment: não aceita dois "+" seguidos
Match a single character present in the list below
[_A-Za-z0-9-\+]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
_ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
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 4310 (2B16 or 538) literally (case sensitive)
1st Capturing Group
(\.[_A-Za-z0-9-]+)*
* 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
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Match a single character present in the list below
[_A-Za-z0-9-]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
_ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
# username @
username
Comment: username
@ matches the character @ with index 6410 (4016 or 1008) literally (case sensitive)
# arroba
arroba
Comment: arroba
Match a single character present in the list below
[A-Za-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 65) and Z (index 90) (case sensitive)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
2nd Capturing Group
(\.[A-Za-z0-9]+)*
* 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
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Match a single character present in the list below
[A-Za-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 65) and Z (index 90) (case sensitive)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
3rd Capturing Group
(\.[A-Za-z]{2,})
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Match a single character present in the list below
[A-Za-z]
{2,} matches the previous token between 2 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 65) and Z (index 90) (case sensitive)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
$ asserts position at the end of a line
Comment: domínio
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)
x modifier: extended. Spaces and text after a # in the pattern are ignored
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gmx

Test String

Code Generator

Generated Code

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Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report.
For a full regex reference for Rust, please visit: https://docs.rs/regex/latest/regex/