How do I run your code?

If you're on windows:

c:\>perl -nle"push @{$h{$_}},$ARGV}{print qq[$_ found in @{$h{$_}}] fo
+r keys %h" 0.dat 1.dat 2.dat 3.dat 4.dat 5.dat 6.dat 7.dat 8.dat 9.da
+t
[download]

On *nix this might work:

$perl -nle'push @{$h{$_}},$ARGV}{print "$_ found in @{$h{$_}}" for key
+s %h' ?.dat
[download]

Is it possible to put this in a .pl file form?

Yes:

#! perl -nl

push @{ $h{ $_ } }, $ARGV

}{

print qq[$_ id in @{$h{ $_ }}] for keys %h;
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Assuming your files are name 0.dat, 1.dat etc.

On windows:

c:\>theScript.pl 0.dat 1.dat 2.dat 3.dat 4.dat 5.dat 6.dat 7.dat 8.dat
+ 9.dat
[download]

On *nix, something like:

$perl theScript.pl ?.dat
[download]