Test a PERL (5.018002) regular expression

Regular Expression (i.e /regex/isg)

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Regular Expressions

Each character matches itself, unless it is one of the special characters + ? . * ^ $ ( ) [ ] { } | \. The special meaning of these characters can be escaped using a \.

. matches an arbitrary character, but not a newline unless it is a single-line match (see m//s).
(...) groups a series of pattern elements to a single element.
^ matches the beginning of the target. In multiline mode (see m//m) also matches after every newline character.
$ matches the end of the line. In multiline mode also matches before every newline character.
[ ... ] denotes a class of characters to match. [^ ... ] negates the class.
( ... | ... | ... ) matches one of the alternatives.
(?# TEXT ) Comment.
(?: REGEXP ) Like (REGEXP) but does not make back-references.
(?= REGEXP ) Zero width positive look-ahead assertion.
(?! REGEXP ) Zero width negative look-ahead assertion.
(? MODIFIER ) Embedded pattern-match modifier. MODIFIER can be one or more of i, m, s, or x.

Quantified subpatterns match as many times as possible. When followed with a ? they match the minimum number of times. These are the quantifiers:

+ matches the preceding pattern element one or more times.
? matches zero or one times.
* matches zero or more times.
{N,M} denotes the minimum N and maximum M match count. {N} means exactly N times; {N,} means at least N times.

A \ escapes any special meaning of the following character if non-alphanumeric, but it turns most alphanumeric characters into something special:

\w matches alphanumeric, including _, \W matches non-alphanumeric.
\s matches whitespace, \S matches non-whitespace.
\d matches numeric, \D matches non-numeric.
\A matches the beginning of the string, \Z matches the end.
\b matches word boundaries, \B matches non-boundaries.
\G matches where the previous m//g search left off.
\n, \r, \f, \t etc. have their usual meaning.
\w, \s and \d may be used within character classes, \b denotes backspace in this context.

Back-references:

\1 ... \9 refer to matched subexpressions, grouped with (), inside the match.
\10 and up can also be used if the pattern matches that many subexpressions.

With modifier x, whitespace can be used in the patterns for readability purposes.

[ EXPR =~ ] [ m ] /PATTERN/ [ g ] [ i ] [ m ] [ o ] [ s ] [ x ]
Searches EXPR (default: $_) for a pattern. If you prepend an m you can use almost any pair of delimiters instead of the slashes. If used in array context, an array is returned consisting of the subexpressions matched by the parentheses in the pattern, i.e., ($1,$2,$3,...).
Optional modifiers: g matches as many times as possible; i searches in a case-insensitive manner; o interpolates variables only once. m treats the string as multiple lines; s treats the string as a single line; x allows for regular expression extensions.
If PATTERN is empty, the most recent pattern from a previous match or replacement is used.
With g the match can be used as an iterator in scalar context.
?PATTERN?
This is just like the /PATTERN/ search, except that it matches only once between calls to the reset operator.