Testing for a file type is called "magic" in linux/unix, hence jwkrahn above mentions the magic file that facilitates translating file signatures to file types.

In a linux/unix you may test with the file command: file $fileyouwanttotest

CPAN has File::MimeInfo (and also File::MimeInfo:Magic, but the name is a bit misleading)
and it works like this:

use File::MimeInfo;
my $mime_type = mimetype('perl-5.38.0.tar.gz');
print("$mime_type\n");
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Cheers, Sören

There's also File::MMagic and File::Type, and many more.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]