How do I handle special characters in a Perl regex?

Question

I\'m using a Perl program to extract text from a file. I have an array of strings which I use as delimiters for the text, e.g:

$pat = $arr[1] . \'(.*?)\' . $         


        

Answer 1

Use quotemeta:

$pat = quotemeta($arr[1]) . '(.*?)' . quotemeta($arr[2]);
if ($src =~ $pat) 
    print $1;

Answer 2

quotemeta escapes meta-characters so they are interpreted as literals. As a shortcut, you can use \Q...\E in double-quotish context to surround stuff that should be quoted:

$pat = quotemeta($arr[1]).'(.*?)'.quotemeta($arr[2]);
if($src=~$pat) { print $1 }

or

$pat = "\Q$arr[1]\E(.*?)\Q$arr[2]";  # \E not necessary at the end
if($src=~$pat) { print $1 }

or just

if ( $src =~ /\Q$arr[1]\E(.*?)\Q$arr[2]/ ) { print $1 }

Note that this isn't limited to interpolated variables; literal characters are affected too:

perl -wle'print "\Q.+?"'
\.\+\?

though obviously it happens after variable interpolation, so "\Q$foo" doesn't become '\$foo'.

Answer 3

Try Perl's quotemeta function. Alternatively, use \Q and \E in your regex to turn off interpolation of values in the regex. See perlretut for more on \Q and \E - they may not be what you're looking for.