Storing part of a regex in a variable

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

Hello all, I'm writing a rather complex script for converting C++ code to Pascal. A number of patterns or sub-pattern occur rather often, and therefore, I'm trying to put them into variables for later use. Here are my variables :

$braces = qr/(?<braces>\{ ([^\{\}] | (?&braces))*? \} )/x;
$brackets = qr/(?<brackets>\( ([^\(\)] | (?&brackets))*? \))/x;
$identifier = qr/(?<identifier> \w+($brackets)?( \s*(\.|->)(?&identifi
+er))?)/;
[download]

The $brackets and $braces variables work as I expected, but the $identifier variable doesn't work right, for example :

#This works
$meth_impl =~ s/((?<identifier> \w+($brackets)?( \s*(\.|->)(?&identifi
+er))?)) \s* \. \s* Trim\(\)/Trim($1)/xg; 

#This doesn't match anything:
$meth_impl =~ s/($identifier) \s* \. \s* Trim\(\)/Trim($1)/xg;
[download]

As you can see in the example above, I'm using the $brackets variable in both cases, and it works nicely. Could the problem be that my $identifier variable itself includes the $brackets variable? Do I need to eval it or something to force it to interpolate it correctly? Thanks in advance, Jonathan Neve

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Re: Storing part of a regex in a variable by Anonymous Monk on Jul 25, 2014 at 17:30 UTC
Could the problem be that my $identifier variable itself includes the $brackets variable? Do I need to eval it or something to force it to interpolate it correctly? No. No. `$identifier = qr/(?<identifier> \w+($brackets)?( \s*(\.\|->)(?&identifi +er))?)/;` [download] It seems you forgot /x there. Your last regex (in substitution) looks this when compiled: `(?^:((?^:(?<identifier> \w+... (etc)` And `(?^:` means Starting in Perl 5.14, a "^" (caret or circumflex accent) immediately after the "?" is a shorthand equivalent to "d-imsx". So, whitespace in `<identifier> \w+` [download] is treated literally. At least, that's what I think, considering the absense of any examples of strings to match. Also, stop writing complex regexes on one line. Perl doesn't have to be write-only, you know?	[reply] [d/l] [select]
Re^2: Storing part of a regex in a variable by Anonymous Monk on Jul 25, 2014 at 17:45 UTC
Correction: it looks like this `(?^x:((?^:(?<identifier> \w+` [download] </code> (I also forgot x :) Also, you may find this useful: http://stackoverflow.com/questions/4231382/regular-expression-pattern-not-matching-anywhere-in-string/4234491#4234491	[reply] [d/l]
Re^2: Storing part of a regex in a variable by jonneve (Initiate) on Jul 26, 2014 at 05:19 UTC
I can't believe it was so simple! It all makes a lot more sense now! As for the one-liners... you're right, and that's why I was trying to use variables to split things up : it's a lot more readable that way. Thanks for your help!	[reply]