# Regular Expressions 101

## Flavor

• PCRE2 (PHP >=7.3)
• PCRE (PHP <7.3)
• ECMAScript (JavaScript)
• Python
• Golang
• Java 8

• Match
• Substitution
• List
• Unit Tests

## Tools

/
(^(0?[1-9]|[12][0-9]|3[01])[-]([a-zA-Z]+)[-]((19|20)\d\d))
/
1st Capturing Group
(^(0?[1-9]|[12][0-9]|3[01])[-]([a-zA-Z]+)[-]((19|20)\d\d))
^ asserts position at start of the string
2nd Capturing Group
(0?[1-9]|[12][0-9]|3[01])
1st Alternative
0?[1-9]
0
matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
Match a single character present in the list below
[1-9]
1-9 matches a single character in the range between 1 (index 49) and 9 (index 57) (case sensitive)
2nd Alternative
[12][0-9]
Match a single character present in the list below
[12]
12
matches a single character in the list 12 (case sensitive)
Match a single character present in the list below
[0-9]
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
3rd Alternative
3[01]
3 matches the character 3 with index 5110 (3316 or 638) literally (case sensitive)
Match a single character present in the list below
[01]
01
matches a single character in the list 01 (case sensitive)
Match a single character present in the list below
[-]
- 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!
3rd Capturing Group
([a-zA-Z]+)
Match a single character present in the list below
[a-zA-Z]
+ 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 sensitive)
A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive)
Match a single character present in the list below
[-]
- 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!
4th Capturing Group
((19|20)\d\d)
5th Capturing Group
(19|20)
1st Alternative
19
19
matches the characters 19 literally (case sensitive)
2nd Alternative
20
20
matches the characters 20 literally (case sensitive)
\d matches a digit (equivalent to [0-9])
\d matches a digit (equivalent to [0-9])
Your regular expression does not match the subject string.Try launching the debugger to find out why.

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