replace not working as expected

digirent has asked for the wisdom of the Perl Monks concerning the following question:

I have a problem replacing tekst in a HTML file, I drilled it down to a few lines of code as follows:

#!/usr/bin/perl
$inputstring=qq{startstring <strong>(substring)</strong> endstring};
$t=qq{<strong>(substring)</strong>};
$r=qq{<b>(substring)</b>};

$inputstring=~s/$t/$r/;
print $inputstring;


#The final string should be:

startstring<b>(substring)</b> endstring
[download]

But it isn't changed. When I remove the ( and ) the replacement works well, but I've no influence on the inputstring. So what I want to achive is that $t is handled as a "exact search string" and not as a to be interpreted regular expression. Help is very appreciated.

Comment on replace not working as expected Download Code

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Re: replace not working as expected by toolic (Bishop) on Feb 04, 2014 at 19:26 UTC
quotemeta `$inputstring=qq{startstring <strong>(substring)</strong> endstring}; $t=quotemeta qq{<strong>(substring)</strong>}; $r=qq{<b>(substring)</b>}; $inputstring=~s/$t/$r/; print $inputstring; __END__ startstring <b>(substring)</b> endstring` [download]	[reply] [d/l]
Re: replace not working as expected by Anonymous Monk on Feb 04, 2014 at 19:32 UTC
The `(...)` is being interpreted as a regular expression group. Try: `$inputstring=~s/\Q$t/$r/;` [download] The `\Q` quotes any special characters following it so they lose their special meaning, so your `$t` will be matched literally. For details see quotemeta and perlre.	[reply] [d/l] [select]