Regular Expressions 101

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  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python 2.7
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Function

  • Match
  • Substitution
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  • Unit Tests (6)
/
(?=\.)(?=\d)
/
gm
Positive Lookahead
(?=\.)
Assert that the Regex below matches
\.
matches the character . literally (case sensitive)
{5,} matches the previous token between 5 and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookahead
(?=\d)
Assert that the Regex below matches
\d
matches a digit (equivalent to [0-9])
{2} matches the previous token exactly 2 times
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)

Regular Expression

/
/
gm

Unit Tests

bana12
abc123
airplanes
banan1
123
1234