Yeah, tr would work as a way of converting something to lower case:

$foo =~ tr/A-Z/a-z/;
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And in the spirit of TMTOWTDI:

$foo = "\Lfoo";
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However, this is probably the most sensible way:

$foo = lc $foo;
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Lastly, you could use a case-insensitive regex instead.
For example, if $test is the string you are matching it with:

if ($foo =~ /^$test$/i) { ... }
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