Use lc or uc to normalise the strings you want to compare:

if (lc $var1 ne lc $var2) {
    ...
}
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Note by the way that $a and $b are special variables used by sort and should generally not be used for other purposes - even in example code.

perlfunc, perlintro, super search

Are you aware that $a and $b are special variables (see perlvar) used by sort. Unless you are using them in that context, you would be well advised to pick different variable names.

The condition you're after can be written as:

if (lc($var1) ne lc($var2)) { ... }
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use Modern::Perl;

while (my $first = <DATA>) {
    my $second = <DATA>;
    chomp $first;
    chomp $second;
    say "Is >$first< equal to >$second<? ", ($first =~ m/^$\Qsecond\E$
+/i)?'Yes':'No';
}

__DATA__
test
TEST
testing
testing
TESTED
TESTED
TeStS
tEsTs
a Test
another Test
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Is >test< equal to >TEST<? Yes
Is >testing< equal to >testing<? Yes
Is >TESTED< equal to >TESTED<? Yes
Is >TeStS< equal to >tEsTs<? Yes
Is >a Test< equal to >another Test<? No
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You forgot quotemeta :)

m/^\Q$second\E$/i
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Indeed! Thank you for reminding me.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

If you wanted to use Unicode's definition of case insensitivity — they are the experts in this area — you should convert the strings to fold case (not lower case or upper case) and then compare them. The simplest way of doing that is:

$s1 =~ /^\Q$s2\E\z/i
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Like the lc and uc methods, this assumes the string has previously been normalised. All together,

use Unicode::Normalize qw( NFC );

$s1 = NFC($s1);
$s2 = NFC($s2);
$s1 =~ /^\Q$s2\E\z/i
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