$ cat t.pl
#!/usr/bin/perl
use strict; use warnings;

my %H = (a=>1, d=>2);
while (<DATA>) {
    s/\s+$//;
    
    if (exists $H{$_}) { print "$_ exists in hash\n"; }
    else               { print "$_ missing from hash\n"; }
}
__DATA__
a
b
c
d