$_ = 'foo';
$left  = '(.)(.)';
$right = '$1$2$2$1';
s{$left}{"qq{$right}"}ee;
print "$_\n";
s{$left}{eval "qq{$right}"}e;
print "$_\n";
__END__
foofo
foofofo

[download]

first /e turns "" into a string qq{$1$2$2$1}

second /e interpolates qq{$1$2$2$1} at the correct time and substitutes into the original string

string eval is eval so arbitrary code could be executed

So, to make it safer, instead of eval ... use some form of String::Interpolate/String::Interpolate::RE

In reply to Re^2: Regex stored in a scalar ( s///eeval ) by Anonymous Monk
in thread Regex stored in a scalar by OtakuGenX

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