The recommendation these days is to use the three argument form of open, lexical filehandles rather than package filehandles (i.e. $fh rather then IN) and to check for the success of the operation, showing the O/S error ($!) in the error message on failure.

...
my $inputFile = q{/path/to/myFile;
open my $inputFH, q{<}, $inputFile
   or die qq{open: < $inputFile: $!\n};
...
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I hope this is helpful.