You can simplify that by using the Tie::File module:

#!/usr/bin/perl
use warnings;
use strict;
use Tie::File;

my $ffdb = 'ffdb.dat';
tie my @ffdbdata, 'Tie::File', $ffdb
    or die "Cannot open $ffdb: $!";

print "Enter ID \n";
my $ID = <STDIN>;
chomp $ID;

if ( $ID eq '' ) {
    die "Cant be empty!\n";
    }

foreach ( @ffdbdata ) {
    s!(?<=^$ID\|)(?:IN|OUT)$!@{[ /IN/ ? 'OUT' : 'IN' ]}!
        and last;
    }
untie @ffdbdata;
exit 0;
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