# first, tell perl you want a local version of a hash called filename
my %filename;

# put in the data for your states 
%filename ( state1 => "FileA.csv",
            state2 => "FileB.csv",
            state3 => "FileC.csv");

# The above statement is the same as writing the three commented lines below. It's prefered because it's simpler, and requires less typing, so it has lower odds for a mistake. Perhaps the lines below are clearer to a beginner, though... they do the same thing as the line above.

#$filename{"state1"}="FileA.csv";
#$filename{"state2"}="FileB.csv";
#$filename{"state3"}="FileC.csv";

# get your state variable somehow... say from a function called get_state()
$state = get_state();

$file = $filename{ $state };

# The above statement a just looks for a matching value for $state in the hash. If it can't find one, uses the undefined value instead. It assigns whatever value it came up with to $file. It's like writing the following big if statement, but again, with less repetition...

# if ( $state eq "state1" ) {
#     $file = "FileA.csv";
# } elsif ( $state eq "state2" ) {
#     $file = "FileB.csv";
# } elsif ( $state eq "state3" ) {
#     $file = "FileC.csv";
# } else {
#     $file = undef();
# }