CODEWITHSUNDEEP
regexperl
xyz
xyz

Reputation: 8917

What is going wrong in this perl substitution?

my $test = "_.4.1\n";
print $test;
my $docid=4;
$test =~ s/_.$docId.1/_.$docId.0/gm;
print $test

I was hoping to see:

_.4.1

_.4.0

But I get:

_.4.1

_.4.1

Upvotes: 1

Views: 110

Answers (3)

brian d foy
brian d foy

Reputation: 132811

Perl 5.10 has a nice feature that makes this problem easier. a \K in the pattern portion of the substitution operator tells it to not replace anything before the \K. That way, you can make the pattern to locate the bit that you want to change, but then only replace the part that doesn't change:

use v5.10;
use strict;
use warnings;

my $test = "_.4.1";
say $test;

my $docId=4;
$test =~ s/_\.$docId\.\K1/0/;

say $test;

I removed the /g and /m flags because they don't do anything in your example.

If you aren't using v5.10 yet (and it's one of the unsupported versions now), you can get the same effect with a positive lookbehind (as long as it's a constant width pattern):

use strict;
use warnings;

my $test = "_.4.1";
print "$test\n";

my $docId = 4;
$test =~ s/(?<=_\.$docId\.)1/0/;

print "$test\n";

Upvotes: 1

TLP
TLP

Reputation: 67900

You have a capital I in $docId in your regex, but declare it with a lower case i. $docid is not considered the same variable as $docId. Perl differentiates between upper and lower case inside variable names.

You should always use

use strict;
use warnings;

To prevent simple errors like this.

See also: Why use strict and warnings?

Upvotes: 8

Nikodemus RIP
Nikodemus RIP

Reputation: 1379

Try using the -w option in perl

_.4.1
Use of uninitialized value $docId in regexp compilation at test.pl line 4.
_.4.1


$docid != $docId;

Upvotes: -1

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