Perl replace value without updating array

Question

I have the following Perl script.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @fruits = qw(apple banana orange pear);

print Dumper \@fruits;

foreach my $fruit (@fruits) {
  $fruit =~ s|apple|peach|;
}

print Dumper \@fruits;

The following is returned.

$VAR1 = [
          'apple',
          'banana',
          'orange',
          'pear'
        ];
$VAR1 = [
          'peach',
          'banana',
          'orange',
          'pear'
        ];

I do not understand why the following line has changed apple to peach in the @fruits array, as I thought this line would only apply to the $fruit variable, not the @fruits array.

$fruit =~ s|apple|peach|;

Donat · Accepted Answer · 2021-07-30 11:43:06Z

5

In the html doc of perl we have the following statement for foreach loops:

the foreach loop index variable is an implicit alias for each item in the list that you're looping over

This means, you do not get a copy of each array element. The variable $fruit is only a reference to an array element. Its value can be modified if the array element can be modified. The modification applies to the original array element.

edited Jul 30, 2021 at 11:43

answered Jul 30, 2021 at 11:37

Donat

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3 Comments

JeremyCanfield Over a year ago

Got it, makes sense now. Within the foreach loop, I will define my $inner = $fruit; and then apply the modification to the $inner variable $inner =~ s|apple|peach|g;. Thanks much for the assistance here!

David Precious Over a year ago

You could use the /r regex modifier to do it in one go, e.g. my $inner = $fruit =~ s|apple|peach|gr; (although I find s{apple}{peach}gr a more readable way personally))

ikegami Over a year ago

If you did get a copy, the code would do nothng

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