if($tmp eq 'F'){
        ;    # do nothing, spot held for clarity
    }elsif($tmp =~ /[MICL]/){
        ...  # do something ...
    }else{
        ...  # do something 
    }
}
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If you have a few different cases, an if/elsif/else chunk like this one is fine, but if you have a lot of possibilities, you should consider building a dispatch table: fill a hash with subrefs and do something like (untested)

$tmp = $some_result;
my $handler = $handlers{$tmp};
&$handler(...) if $handler; # might be undef, as in 'F' case
[download]

This has the disadvantage of failing silently if you get an unexpected value in $tmp; you could fix it by giving 'F' a do-nothing subroutine and raising an error if $handler is undefined.