foreach my $line ( <$input_fh> )

should be

while (my $line = <$input_fh> )

The first form is a glob, (but I don't know well enough to explain it to you).

The second line should work properly for reading your file.

Update: Yes Choroba is correct, it is not a glob - my mistake,

In reply to Re^3: Shorten the headers of a file and remove empty lines using perl by Cristoforo
in thread Shorten the headers of a file and remove empty lines using perl by intect

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