grep Question

Shivam05 has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am trying to grep label(" in the array, it will generate error while executing . sample code:

$grepper=join('','label','(','"');
print "$grepper\n";
$array[0]="label(";
$array[1]="label";

@LABEL = grep(/$grepper/, @array);
print "@LABEL \n";
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And also, i tried this line directly:

@LABEL = grep(/label\(\"/, @array);
print "@LABEL \n";
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if i use this it does not take " correctly in the label(". How can i over come the problemand solution for this.

--Shiva Prasad.

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Re: grep Question
by Athanasius (Archbishop) on May 20, 2015 at 07:27 UTC

Hello Shivam05, and welcome to the Monastery!

Your code has two problems. First, you need to disable the metacharacters in $grepper when using it in a regular expression:

my @LABEL = grep(/\Q$grepper\E/, @array);
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See quotemeta.

Second, as others have noted, you set the value of $array[0] to label(, which does not contain the double-quote character. Therefore, the regular expression finds nothing to match in @array. You can fix this in several ways:

$array[0] =   "label(\"";
$array[0] =   'label("';
$array[0] = qq{label("};
$array[0] =  q{label("};
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See perlop#Quote-and-Quote-like-Operators

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re: grep Question
by Happy-the-monk (Canon) on May 20, 2015 at 07:26 UTC

To elaborate on Utilitarian's response:

Your array contains both label" (with " ) and label( ( with ( ) .

You fail to match label(" (with ( and " ) in the array because it is not there.

Cheers, Sören

Créateur des bugs mobiles - let loose once, run everywhere.
(hooked on the Perl Programming language)

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Re: grep Question
by GrandFather (Saint) on May 20, 2015 at 07:40 UTC

Generally it helps us help you if you show the error generated by running the program.

It will also help you track down problems if you always use strictures (use strict; use warnings;). I appreciate the code shown may be a fragment of something larger, but just to make sure you are aware of a couple of coding techniques, here's a "tidied" version of your code:

use strict;
use warnings;

my $grepper = 'label("';
print "$grepper\n";

my @array = ("label(", "label");
my @LABEL = grep {/\Q$grepper\E/} @array;

print ">@LABEL<\n";
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Note the updated final print to make it clear that the array is empty.

Perl is the programming world's equivalent of English

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Re: grep Question
by Utilitarian (Vicar) on May 20, 2015 at 07:20 UTC

'label(' ne 'label("'

print "Good ",qw(night morning afternoon evening)[(localtime)[2]/6]," fellow monks."

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Re: grep Question
by soonix (Canon) on May 20, 2015 at 10:30 UTC

~~either~~

character class

use strict;
use warnings;
use Data::Dumper;

my $grepper = 'label[("]';
my @array = qw ! label( label" label% label!;
my @LABEL = grep /$grepper/, @array;

print Dumper $grepper, \@array, \@LABEL;
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$VAR1 = 'label[("]';
$VAR2 = [
          'label(',
          'label"',
          'label%',
          'label'
        ];
$VAR3 = [
          'label(',
          'label"'
        ];
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