If that's for a one-off script, you appear to have your answer. For a solution that's to be used in the longer term, you might consider something along the lines of the following skeleton code:

In a module, say Medical.pm:

package Medical;
sub new { ... }
sub allergies { ... }
sub immunizations { ... }
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Then, in your script:

use Medical;
my $medical = Medical->new();
...
$medical->$filename();
...
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When you later need to process a new file, say diseases, you don't need to update a dispatch table or change your script in any way. Just add sub diseases { ... } to Medical.pm.