$hash{a} may either valuate to a scalar or an array reference but not both, at least not in the way you present - Perl is trying to interpret bob as an array reference and bombing out with a slightly confusing error message. I would tend to make it always valuate to an array reference, even if there is only one value, e.g.
use strict;
use warnings;

my $cfg = ARGV[0]
  or die "Usage: $0 <config_file>\n";
my %hash;
open my $ch, $cfg
  or die "$!: $cfg\n";
while( <$ch> ) {
    chomp;
    my ($k, $v) = split /\s+/;
    $hash{k} ||= [];
    push @{ $hash{$k}}, $v;
}
close $ch;

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In reply to Re: Extending a hash by anonymized user 468275
in thread Extending a hash by dingbob

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