Regular Expressions 101

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  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python 2.7
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"
^(?:[\w \/]*\:(?:(?!\n\n|\n[\w ]+\:).)*)|\* \* \*
"
gms
1st Alternative
^(?:[\w \/]*\:(?:(?!\n\n|\n[\w ]+\:).)*)
^ asserts position at start of a line
Non-capturing group
(?:[\w \/]*\:(?:(?!\n\n|\n[\w ]+\:).)*)
Match a single character present in the list below
[\w \/]*
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\w matches any word character (equal to [a-zA-Z0-9_])
matches the character literally (case sensitive)
\/ matches the character / literally (case sensitive)
\: matches the character : literally (case sensitive)
Non-capturing group
(?:(?!\n\n|\n[\w ]+\:).)*
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Negative Lookahead
(?!\n\n|\n[\w ]+\:)
Assert that the Regex below does not match
1st Alternative
\n\n
2nd Alternative
\n[\w ]+\:
. matches any character
2nd Alternative
\* \* \*
\* matches the character * literally (case sensitive)
matches the character literally (case sensitive)
\* matches the character * literally (case sensitive)
matches the character literally (case sensitive)
\* matches the character * literally (case sensitive)
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)
s modifier: single line. Dot matches newline characters
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"
gms

Test String

Regular Expressions 101

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