I'm assuming you're talking about CGI here, and that you're talking about the value of a form element. In this case, something like lc might be what you need:

use CGI;

my $value = param('field');      # "mY vALuEs RuLE"
   $value = lc(param('field'));  # "my values rule"
   $value = uc(param('field'));  # "MY VALUES RULE"
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