It would help if your code was properly formatted. Anyway, to use 'say' you need to

use v5.10;
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for "my $debug" declaration you probably meant

my $debug = $ARGV[1];
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'ids' need to be declared as a hash, not a scalar

my %ids;
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while loop needs to read from the file handle that you opened instead of checking the truth value of $filename variable which causes infinite loop if $filename is anything other than 0 or empty string

while(<IN>)
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'print say' at the end doesn't really do any good