Double Interpolation in // operator?

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

Here's some code:

#!/usr/bin/perl -w
use strict;
sub FOO {
    return qw($bar $foobar);
}
my $foo = '$bar';
print "It matched!\n" if (grep /$foo/, FOO());
[download]

This fails, even though it should work. And this code works if i change this line:

my $foo = '\$bar';
[download]

Which looks (to me) like /$foo/ is interpolating $foo twice. Why is this?

BlueLines

Disclaimer: This post may contain inaccurate information, be habit forming, cause atomic warfare between peaceful countries, speed up male pattern baldness, interfere with your cable reception, exile you from certain third world countries, ruin your marriage, and generally spoil your day. No batteries included, no strings attached, your mileage may vary.

Comment on Double Interpolation in // operator? Select or Download Code

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Re: Double Interpolation in code///code operator? by japhy (Canon) on May 24, 2001 at 23:00 UTC
Please look at your regex. When you do `/$foo/`, it interpolates `$foo` to the string '$bar'. This makes your regex try to match end-of-line ($), followed by 'bar'. That can't happen. If `$foo` is '\$bar', then you have a different case. You try to match '\$', which is a literal dollar-sign, followed by 'bar'. That works. Watch: friday:~ $ perl -mre=debug $re = '$bar'; print map ">$_\n", grep /$re/, qw( $foo $bar ); compiling RE `$bar' size 5 first at 1 1: EOL(2) 2: EXACT <bar>(5) 5: END(0) anchored `bar' at 0 (checking anchored) minlen 3 Matching `$bar' against `bar' Setting an EVAL scope, savestack=12 1 <$> <bar> \| 1: EOL friday:~ $ perl -mre=debug $re = '\$bar'; print map ">$_\n", grep /$re/, qw( $foo $bar ); compiling RE `\$bar' size 4 first at 1 1: EXACT <$bar>(4) 4: END(0) anchored `$bar' at 0 (checking anchored isall) minlen 4 >$bar [download] `japhy` -- Perl and Regex Hacker	[reply] [d/l]
Re: Re: Double Interpolation in code///code operator? by BlueLines (Hermit) on May 24, 2001 at 23:05 UTC
forehead smack I spent two hours last night pouring over this, and that never occured to me. ++ and thanks. BlueLines Disclaimer: This post may contain inaccurate information, be habit forming, cause atomic warfare between peaceful countries, speed up male pattern baldness, interfere with your cable reception, exile you from certain third world countries, ruin your marriage, and generally spoil your day. No batteries included, no strings attached, your mileage may vary.	[reply]


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