# Regular Expressions 101

## Flavor

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

• Match
• Substitution
• List
• Unit Tests

## Tools

"
(\d+\.([1-9]{3}|[1-9]{2}|[1-9]|0{1}))(\d*)
"
gm
1st Capturing Group
(\d+\.([1-9]{3}|[1-9]{2}|[1-9]|0{1}))
\d
matches a digit (equivalent to [0-9])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
2nd Capturing Group
([1-9]{3}|[1-9]{2}|[1-9]|0{1})
1st Alternative
[1-9]{3}
Match a single character present in the list below
[1-9]
{3} matches the previous token exactly 3 times
1-9 matches a single character in the range between 1 (index 49) and 9 (index 57) (case sensitive)
2nd Alternative
[1-9]{2}
Match a single character present in the list below
[1-9]
{2} matches the previous token exactly 2 times
1-9 matches a single character in the range between 1 (index 49) and 9 (index 57) (case sensitive)
3rd Alternative
[1-9]
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)
4th Alternative
0{1}
0
matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
3rd Capturing Group
(\d*)
\d
matches a digit (equivalent to [0-9])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
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.

r"
"
gm