See perlre, and search for insensitive.

if ($array_A[$ds] =~ /test/i)
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There is also:

/(?i:test)/

This is especially useful if you want part of the pattern case-sensitive and part not. For example, the first letter may be upper or lowercase but the rest must be lowercase.

/(?i:t)est/

I would add that if you are manually processing each element of the array, you may be doing it the hard way:

#!/usr/bin/perl
# testgreparray.pl - Check behavior of grep on arrays

use strict;

my @cmdrsp = (
    'This is a test.',
    'A booger a day keeps the doctor at bay.',
    'Blimey, laddy, it\'s a booger!'
);

if (grep(/booger/, @cmdrsp)) {
    print "Found it the easy way\n";
}

my @searsp = grep(/booger/, @cmdrsp);
my $seacnt = @searsp;
if ($seacnt) {
    print "Found it the hard way\n";
}
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It seems everyone is quite fond of the /i modifier, not to mention their CPU cycles. In colder climates, I find the following helps keep toes warmer, longer:

#!/usr/bin/env perl

use 5.012;
use warnings;
use Carp;

say insensitive('This is a test', qr/this is a test/) ? 'Match!' : 'No
+ match.';

sub insensitive {
    my ($cmp, $re) = @_;
    croak "expecting regexp, got " . ref $re unless 'Regexp' eq ref $r
+e;
    carp "Insensitive use of uninitialized value" unless defined $cmp;

    my ($len, %seen) = length($cmp);
    croak "Not without bignum" if $len > 31;
    while (keys %seen <= 2**$len) {
        return 1 if $cmp =~ $re;
        substr($cmp, int rand $len, 1) ^= ' ';
        undef $seen{$cmp};
    }
    return;
}
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Unicode support is left as an exercise to the reader.

How about doing it more directly? The obvious solution seems to be to compare against /test|Test|tEst|.../. The glob function will help to create such a pattern:

use strict;
use warnings;

my $pat = "test";
$pat = join "|", glob join "", map { "{".uc.",".lc."}"} split //, $pat
+;
print "$pat\n";

for ( qw( Test test tesT tast ) ) {
    print "$_\n" if /$pat/;
}
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You really prefer this solution over adding a single "i" to the regex?

You really prefer this solution over adding a single "i" to the regex?

You really didn't know my post was a joke?