#!/usr/bin/perl

$tempstr = qq`
[IF a = /1/
1
ELSIF b = /2/
2
ELSE
3
]
`;

my $reg = qr{\[(?:(?>[^\[\]]+)|(??{$reg}))*\]};
$tempstr =~ s/\[(?:IF|ELSIF|ELSE)(\s+\S+\s*\=\s*.*?)?\n((?:$reg|\n|[^\
+[\]])+\])/iffer($1,$2)/ges;


sub iffer {
my $test = shift;
$test .= shift;
print "trying iffer... test: $test\n";
my $reg = qr{\[(?:(?>[^\[\]]+)|(??{$reg}))*\]};
$test =~ s/(?:(?:$reg|\n|[^\[\]])+?)(^(?:ELSIF|ELSE\s*\n).*\]|\])/\[$1
+/sm;
return $test;
}

[download]

The above code runs "iffer" once and results in:

$ ./t.pl
trying iffer... test:  a = /1/1
ELSIF b = /2/
2
ELSE
3
]
$

[download]

The following code, with the only difference being the inclusion of the while loop, results in a different (and desired) result:

#!/usr/bin/perl

$tempstr = qq`
[IF a = /1/
1
ELSIF b = /2/
2
ELSE
3
]
`;

my $reg = qr{\[(?:(?>[^\[\]]+)|(??{$reg}))*\]};
while ($tempstr =~ s/\[(?:IF|ELSIF|ELSE)(\s+\S+\s*\=\s*.*?)?\n((?:$reg
+|\n|[^\[\]])+\])/iffer($1,$2)/ges) {}


sub iffer {
my $test = shift;
$test .= shift;
print "trying iffer... test: $test\n";
my $reg = qr{\[(?:(?>[^\[\]]+)|(??{$reg}))*\]};
$test =~ s/(?:(?:$reg|\n|[^\[\]])+?)(^(?:ELSIF|ELSE\s*\n).*\]|\])/\[$1
+/sm;
return $test;
}

[download]

And the results:

$ ./t.pl
trying iffer... test:  a = /1/1
ELSIF b = /2/
2
ELSE
3
]
trying iffer... test:  b = /2/2
ELSE
3
]
trying iffer... test: 3
]
$

[download]

Can someone help me understand why these two result in two totally different results? Shouldnt the inclusion of the /g modifier in the first ensure that the pattern is matched repeatedly (i.e., the ELSIF and then ELSE patterns match)... (The complexity of the regular expressions are to account for the possibility of nested conditionals in my own "mini-language".)

In reply to Complex regex and apparent failure of /g option by lokiloki

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