perl function to parse the command output - regex

Question

I have written a perl function that executes a command and parses the command output. The command will provide the output mentioned below. In the function call i pass a number between 1 to 5 as arguments . '1' correspond to lan, 2 corresponds to wan, '3' corresponds to name and so on. ( see the output below) . for example if 1 is passed as an argument in the function call the expected output is '0' ( 1 = lan and value of lan = 0 ) . When i execute the script im not getting the expected output. null is returned.Any suggestions?
command output 1 :
[
{
"lan" : 0, #1
"wan" : 0, #2
"name" : "XYZ", #3
"packets" : 0, #4
"bytes" : 0 #5
}
]
Function call
$self->{'stats_obj'} = Statistics->new( ip => "ip addr")
my $result = $self->{'stats_obj'}->statistics_get('1');
INFO('statistics:' . $result );
Function:
sub statistics_get{
my ($self, $option)= #_;
my $result = $self->_get_hyd_tc();
return $result->{$option};
}
sub _get_hyd_tc {
my ($self) = #_;
my $opt;
my %result;
my $line;
my $cmd = 'cmd goes here';
$self->execute($cmd);
my $count =0;
foreach my $line ( $self->output() ) {
chomp $line;
if ( $line =~ /(Requested table doesn't.*)/i ){
ERROR('table doesnt exist' . $line)
}
if ($line =~ /(.*)/) {
$opt = $1;
$count = 0;
}
elsif ( $line =~ /(.*)/) {
my $key = $1;
my $value = $2;
$result{$opt}{++$count} = $value;
}
}
return \%result;
}

Answer 1

You are approaching this the wrong way.
Your snippet you give is JSON. So really - your best bet by far is to process it as JSON and not try and parse it yourself.
Something like this:
use strict;
use warnings;
use JSON;
use Data::Dumper;
my $command_output = '[
{
"lan" : 0,
"wan" : 0,
"name" : "XYZ",
"packets" : 0,
"bytes" : 0
}
]';
my $json_ob = decode_json( $command_output );
print Dumper \$json_ob;
print $json_ob -> [0] -> {'name'};
Those [] in your text denotes an array. usually that means multiple elements. You could iterate those elements, but as you've just got one, accessing it via [0] does the trick.
Now, you could if you really want map the attributes from 'words' to numeric, but ... there isn't really any need.
But to answer your question - why is null returned - it's because:
if ($line =~ /(.*)/) {
Will always evaluate as true - zero or more of anything.
And therefore you will never run the second elsif loop and so this never happens:
$result{$opt}{++$count} = $value;
And so you never have anything other than an empty array to return.