Regular Expressions 101

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  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
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/
(href=")(?!\/|http(s)?)
/
g
1st Capturing Group
(href=")
href=" matches the characters href=" literally (case sensitive)
Negative Lookahead
(?!\/|http(s)?)
Assert that the Regex below does not match
1st Alternative
\/
\/ matches the character / literally (case sensitive)
2nd Alternative
http(s)?
http matches the characters http literally (case sensitive)
2nd Capturing Group
(s)?
? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)
s matches the character s literally (case sensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/
g

Test String