Regular Expressions 101

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/
^\s*(true|false)\s*$
/
gm
^ asserts position at start of a line
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
1st Capturing Group
(true|false)
1st Alternative
true
true
matches the characters true literally (case sensitive)
2nd Alternative
false
false
matches the characters false literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
* matches the previous token between zero 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)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gm

Test String

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For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php