sub slurp {
        my $fname = shift;
        open my $FILE, '<', $fname;
        local $/;
        my $key = <$FILE>;
close $FILE;
        return $key;
}
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You should verify that the file opened correctly and take appropriate action if it didn't rather than trying to use a possibly invalid filehandle.

You should chomp the data returned here rather than in another subroutine.

sub slurp {
        my $fname = shift;
        local $/;
        open my $FILE, '<', $fname or die "Cannot open '$fname' becaus
+e: $!";
        chomp( my $key = <$FILE> );
        return $key;
}
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sub has_key {
        my ($key, $keys) = @_;
        chomp($key);
        my $suc = 0;
        my @keys = split /\n/,$keys;
        my $i = 1;
        foreach my $k (@keys) {
                chomp($k);
                if($key eq $k) {
                        $suc = 1;
                        last;
                } else {
                        $suc = 0;
                }
                $i++;
        }
        return $suc;
}
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The $i variable is superfluous in this subroutine.

You are spliting, and thus removing newlines from @keys and then you are chomping the elements of @keys to remove newlines that aren't there anymore?

The else clause in the loop is totally superfluous because you exit the loop as soon as you change the value of $suc.

sub has_key {
        my ( $key, $keys ) = @_;
        foreach my $k ( split /\n/, $keys ) {
                return 1 if $key eq $k;
        }
        return 0;
}
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Or:

sub has_key {
        my ( $key, $keys ) = @_;
        return scalar grep $key eq $_, split /\n/, $keys;
}
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