Can I use Q and E to regex match the dollar sign?

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

Monks, I thought \Q and \E in regexes means no interpolation happens, like the equivalent of '' for strings. But I guess I was wrong about that as the following snippet shows. Or is there indeed some way to get \Q and \E to literal-match the dollar, as it literal-matches parenthesis and most other special characters? Thanks!

use strict;
use warnings;
use Test::More qw(no_plan);

like('a',qr/a/); #passes
like('(',qr/\Q(\E/); #passes -- \Q\E works for parenthesis and most sp
+ecial characters
like('asdf$',qr/\Qasdf$\E/); #no -- but not for the dollar sign
like('asdf$',qr/\Qasdf\$\E/); #no
like('asdf$',qr/asdf$/); #no
like('asdf$',qr/\$/); #passes -- you have to backslash the dollar
[download]

UPDATE: Much obliged, monks. Cutting to the good part, it seems my question can best be answered with: use quotemeta, and compile the result with qr.

use strict;
use warnings;
use Test::More qw(no_plan);

like('asdf$', quotemeta('asdf$')); #fails
my $re = quotemeta('asdf$'); 
like('asdf$', qr/$re/); #passes
like('asdf$', qr/@{[ quotemeta('asdf$') ]}/); #passes
[download]

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Re: Can I use Q and E to regex match the dollar sign? by borisz (Canon) on Aug 30, 2005 at 18:21 UTC
from the docs perldoc perlre: `You cannot include a literal "$" or "@" within a "\Q" sequence. An unescaped "$" or "@" interpolates the corresponding variable, while escaping will cause the literal string "\$" to be matched. You'll need to write something like "m/\Quser\E\@\Qhost/".` Boris	[reply]
Re^2: Can I use Q and E to regex match the dollar sign? by radiantmatrix (Parson) on Aug 30, 2005 at 19:36 UTC
So, in other words, the OP would have to move the literal `$` outside the `\Q\E` set, like this: `like('asdf$',qr/\Qasdf\E\$/);` [download] The other option, of course, would be something like: `## matches a literal '[a-z]$[0-9]' using quoting like( '[a-z]$[0-9]', quotemeta('[a-z]$[0-9]') );` [download] (As ikegami pointed out above) <-radiant.matrix-> Larry Wall is Yoda: there is no `try{}` (ok, except in Perl6; way to ruin a joke, Larry! ;P) The Code that can be seen is not the true Code "In any sufficiently large group of people, most are idiots" - Kaa's Law	[reply] [d/l] [select]
Re: Can I use Q and E to regex match the dollar sign? by ikegami (Patriarch) on Aug 30, 2005 at 18:37 UTC
No, `\Q...\E` doesn't escape `$` and `@`. You can use `quotemeta` instead: `like('asdf$', quotemeta('asdf$'));` [download] If you absolutely need to compile the regexp before calling `like` (doubtful), here are some possible calling syntaxes: `$re = quotemeta('asdf$'); like('asdf$', qr/$re/); -or- like('asdf$', qr/@{[ quotemeta('asdf$') ]}/); -or- like('asdf$', map { qr/$_/ } map quotemeta, 'asdf$');` [download]	[reply] [d/l] [select]