Perl backticks in hash ref giving different results

Question

I have a file called a.gz which is a gzipped file which contains the following lines when unzipped:

a
b

Below are two blocks of perl code which I think "should" give the same results but they don't.

Code #1:

use Data::Dumper;
my $s = {
        status => 'ok',
        msg    => `zcat a.gz`
};
print Dumper($s),"\n";

Code #2:

use Data::Dumper;
my $content = `zcat a.gz`;
my $s = {
      status => 'ok',
      msg    => $content
};
print Dumper($s), "\n";

Code #1 gives the following result:

Odd number of elements in anonymous hash at ./x.pl line 8.
$VAR1 = {
          'msg' => 'a
',
          'b
' => undef,
          'status' => 'ok'
        };

Code #2 returns the following result:

$VAR1 = {
          'msg' => 'a
b
',
          'status' => 'ok'
        };

I'm using perl 5.10.1 running in Linux

melpomene · Accepted Answer · 2016-06-04T15:56:47.187

perldoc perlop:

In scalar context, it comes back as a single (potentially multi-line) string, or undef if the command failed. In list context, returns a list of lines (however you've defined lines with $/ or $INPUT_RECORD_SEPARATOR), or an empty list if the command failed.

Assigning to a scalar puts `` in scalar context; using it in { ... } puts it in list context.

{ LIST } takes a list and interprets its contents alternating between keys and values, i.e. key1, value1, key2, value2, key3, value3, .... If the number of elements is odd, you get a warning (and the missing value is taken to be undef).

LIST , LIST (the comma operator in list context) concatenates two lists.

=> works just like , but automatically quotes the identifier to its left (if there is one).

Thanks. I wasn't aware that key/value assignment within `{....}` is array context. I thought that values are always scalar. Thanks for pointing this out. — fat_apupu, Jun 04 '16 at 15:51

Perl backticks in hash ref giving different results

1 Answers1