Regular Expressions 101

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PCRE2 (PHP >=7.3)
PCRE (PHP <7.3)
ECMAScript (JavaScript)
Python 2.7
Golang (RE2)

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^\d+(?:\.\d+)?$

^ asserts position at start of a line

\d+

matches a digit (equal to [0-9])

+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)

Non-capturing group

(?:\.\d+)?

? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)

\. matches the character . literally (case sensitive)

\d+

matches a digit (equal to [0-9])

+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)

$ asserts position at the end of a line

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 Expressions 101

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Regular Expressions 101

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Regular Expressions 101

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