Regular Expressions 101

Save & Share

Flavor

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

Function

  • Match
  • Substitution
  • List
  • Unit Tests
/
(<a(?:(?!\/a>).|\n)*(?=\>).)(.+)(<\/a>)
/
i
1st Capturing Group
(<a(?:(?!\/a>).|\n)*(?=\>).)
<a
matches the characters <a literally (case insensitive)
Non-capturing group
(?:(?!\/a>).|\n)*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
1st Alternative
(?!\/a>).
Negative Lookahead
(?!\/a>)
Assert that the Regex below does not match
\/ matches the character / with index 4710 (2F16 or 578) literally (case insensitive)
a>
matches the characters a> literally (case insensitive)
. matches any character (except for line terminators)
2nd Alternative
\n
\n matches a line-feed (newline) character (ASCII 10)
Positive Lookahead
(?=\>)
Assert that the Regex below matches
\> matches the character > with index 6210 (3E16 or 768) literally (case insensitive)
. matches any character (except for line terminators)
2nd Capturing Group
(.+)
.
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)
3rd Capturing Group
(<\/a>)
< matches the character < with index 6010 (3C16 or 748) literally (case insensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case insensitive)
a>
matches the characters a> literally (case insensitive)
Global pattern flags
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

/
/
i

Test String