use strict;
my $str = 'NOTE: For test purposes each test has been contained to one line, please enable the s flag for multi-line matches.
$ match $ don\'t match nested $ match $
$$ no match$
$no match$$
\\\\$no match\\\\$
$no match\\\\$
\\\\$no match\\\\$
$$ match $$ don\'t match nested $$ match $$
$$$ no match $$
$$ no match $$$
\\\\$$ no match$$
$$ no match\\\\$$
\\\\$$ no match\\\\$$
\\( match \\)
\\( 1 \\( nested match \\) 3 \\)
\\\\( no match \\\\)
\\( no match \\\\\\\\)
\\\\\\\\( no match \\\\\\\\)
\\[ match \\]
\\[ 1 \\[ nested match \\] 3 \\]
\\\\\\\\[ no match \\\\]
\\\\[ no match \\\\\\\\]
\\\\\\\\[ no match \\\\\\\\]
\\begin{equation} match \\end{equation}
\\begin{equation} 1 \\begin{equation} nested match \\end{equation} \\end{equation}
\\\\\\\\begin{equation} no match \\\\end{equation}
\\\\begin{equation} no match \\\\\\\\end{equation}
\\\\\\\\begin{equation} no match \\\\end{equation}';
my $regex = qr/(?<!\\) # negative look-behind to make sure start is not escaped
(?: # start non-capture group for all possible match starts
# group 1, match dollar signs only
# single or double dollar sign enforced by look-arounds
((?<!\$)\${1,2}(?!\$))|
# group 2, match escaped parenthesis
(\\\()|
# group 3, match escaped bracket
(\\\[)|
# group 4, match begin equation
(\\begin\{equation\})
)
# if group 1 was start
(?(1)
# non greedy match everything in between
# group 1 matches do not support recursion
(.*?)(?<!\\)
# match ending double or single dollar signs
(?<!\$)\1(?!\$)|
# else
(?:
# greedily and recursively match everything in between
# groups 2, 3 and 4 support recursion
(.*(?R)?.*)(?<!\\)
(?:
# if group 2 was start, escaped parenthesis is end
(?(2)\\\)|
# if group 3 was start, escaped bracket is end
(?(3)\\\]|
# else group 4 was start, match end equation
\\end\{equation\}
)
))))/mxp;
if ( $str =~ /$regex/g ) {
print "Whole match is ${^MATCH} and its start/end positions can be obtained via \$-[0] and \$+[0]\n";
# print "Capture Group 1 is $1 and its start/end positions can be obtained via \$-[1] and \$+[1]\n";
# print "Capture Group 2 is $2 ... and so on\n";
}
# ${^POSTMATCH} and ${^PREMATCH} are also available with the use of '/p'
# Named capture groups can be called via $+{name}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html