CODEWITHSUNDEEP
perl
user4711
user4711

Reputation: 21

Replace foreach with grep in perl

I'm new to perl and I tried to replace my foreach-statement (version 1): 

use warnings;
use strict;

$cmd_list = "abc network xyz";
foreach my $item (split(" ", $cmd_list)) {
if( $item eq "network") {
    $PRINT_IP = 1;
    }
}

with a grep (version 2, from some example in the internet) which should give me the count (because of scalar context) of the value "network" in a string array:

$PRINT_IP = grep(/^$network$/, split(" ", $cmd_list));

for version 1 the if statement works as supposed, but for version 2 it always evaluates to false:

if($PRINT_IP) {
    ...
}

Where is my fault?

Upvotes: 0

Views: 454

Answers (1)

zdim
zdim

Reputation: 66944

There seems to be a typo, as $network is a variable; you may mean /^network$/.

Having use strict; in your program would have alerted you to an untended (so undeclared) variable. Having use warnings; would have alerted you to the use of an uninitialized variable in regex compilation.

In the loop you only set the variable $PRINT_TP (to 1) if there are any elements that match. Then List::Util has a function just for that

my $PRINT_IP = any { $_ eq 'network' } split ' ', $cmd_list;

or 

my $PRINT_IP = any { /^network\z/ } split ' ', $cmd_list;

if you need regex for more complex conditions.

This returns 1 on the first match, the result that your for loop produces. If you actually need a count then indeed use grep. When there's no match $PRINT_IP is set to '', an empty string.

The library is more efficient, firstly since it stops processing once a match happens. You can also do that by adding last in your if condition but List::Util routines are generally more efficient.

More importantly: please always have use warnings; and use strict; at the beginning.

Upvotes: 5

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