Unfortunately, the code in the direct parent (and similar offerings above) does not produce what I understand to be OP's intended result. Execution of the code in Re: Regex Matching Query goes like this:

C:\> 1025454.pl
Show name: TEST SHOW S
Show rest: 01E01
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It's my understanding that all after the final space -- i.e., S01E01 -- is the desired output.

So why is the regex a few degrees off plumb? As written the technical greediness of the death star in the first capture is mitigated by the trailing questionmark... but the second capture looks for a digit as its starting point, relegating the "S" to the first capture.

Consider instead the elevated particularity of:

if(my ($show, $file) = $file =~ /(.*?)\s([A-Z]\d+.*)/) {
    print "Show name: $show\n";
    print "Show rest: $file\n";
}
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which outputs:

Show name: TEST SHOW
Show rest: S01E01
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Regexen entirely capable of biting BOTH an excess and an insufficiency of precision in their crafting.