if ($search) { ...

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;

use List::MoreUtils qw{first_index last_index};

my @array_to_search = qw{ 0 2 4 2 0 };

print 'Search: ';
chomp( my $search = <STDIN> );

if (length $search) {
    my $index_1 = first_index { $_ eq $search } @array_to_search;

    if ($index_1 >= 0) {
        my $index_N = last_index { $_ eq $search } @array_to_search;

        print "First occurrence of '$search' at index: $index_1\n";
        print "Last occurrence of '$search' at index: $index_N\n";
    }
    else {
        print "'$search' not found.\n";
    }
}
else {
    print "Nothing to search for!\n";
}

##</code><code>##

Search:  
Nothing to search for!

##</code><code>##

Search: 100
'100' not found.

##</code><code>##

Search: 0
First occurrence of '0' at index: 0
Last occurrence of '0' at index: 4

##</code><code>##

Search: 2
First occurrence of '2' at index: 1
Last occurrence of '2' at index: 3

##</code><code>##

Search: 4
First occurrence of '4' at index: 2
Last occurrence of '4' at index: 2