http://www.perlmonks.org?node_id=1062852

sunil9009 has asked for the wisdom of the Perl Monks concerning the following question:

I have a list of hostclasses each having a list of host, I want to combine all the hosts in the hostclasses to give me an array of hosts. Command "expand-hostclass" gives me a list of hosts with each host as a newline. My problem is that the array considers hosts in each hostclass as a scalar ($hosts_per_hostclass).I want to flatten the scalar ($hosts_per_hostclass) to an array, so that each element in the array is a hostname. Hope I am not confusing too much Please help. I tried the following code

#!/usr/bin/perl
my @hostclass = ('Hostclass-A','Hostclass-B','Hostclass-C');
my @hosts;
my @TotalHosts;
my $class;
my $hosts_per_hostclass;

gethosts();

sub gethosts {
foreach $class(@hostclass) {
$hosts_per_hostclass = `expand-hostclass` ;
push (@TotalHosts,$hosts_per_hostclass);
my @dd = split "\n", @TotalHosts;
print "@dd \n";
}
}

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Re: splitting the scalar variables in an array
by Athanasius (Archbishop) on Nov 16, 2013 at 06:55 UTC

    split expects its second argument to be a string (i.e., a scalar), so using the array @TotalHosts here puts the array into scalar context, and split gets the number of elements in the array. You need to change this line:

    my @dd = split "\n", @TotalHosts;

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    to something like this:

    my   @dd;
push @dd, split "\n", $_ for @TotalHosts;

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    which calls split on each element of the array in turn. This works provided that each of the array elements is a string.

    Hope that helps,

    Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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      my   @dd;
push @dd, split "\n", $_ for @TotalHosts;

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      No need for push and for:

      my @dd=map { split "\n" } @TotalHosts;

      Alexander

      --
      Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
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      Thanks for the help, I modified the code but that didnt helped either. The scalar value for @dd returned by the code is as follows 1 1 4 Thats because Hostclass-A has 1 host, Hostclass B has 1 and C has 4 hosts. I want scalar(@dd) to be just 6 ( each host should be a separate element in an array ) 

      
sub gethosts {

foreach $class(@hostclass) {
chomp (@hosts_per_hostclass = `/opt/systems/bin/expand-hostclass --hos
+ts -r $class`) ;
my @dd;
push @dd, split "\n", $_ for @hosts_per_hostclass;
print scalar(@dd) , "\n";

}
}

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        Consider this resolved, foreach was printing it 3 times. Final working code is as follows. Thanks to all of you guys fo the pointers. 

        sub gethosts {

foreach $class(@hostclass) {

chomp (@hosts_per_hostclass = `/opt/systems/bin/expand-hostclass --hos
+ts -r $class`) ;
#print "@hosts_per_hostclass \n";
push @dd, split "\n", $_ for @hosts_per_hostclass;
}
return @dd;
}

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Re: splitting the scalar variables in an array
by jwkrahn (Abbot) on Nov 16, 2013 at 10:36 UTC 
    $hosts_per_hostclass = `/opt/systems/bin/expand-hostclass --hosts -r $
+class` ;
push (@TotalHosts,$hosts_per_hostclass);

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    Back-quotes in list context return a list so you could do this: 

    chomp( @hosts_per_hostclass = `/opt/systems/bin/expand-hostclass --hos
+ts -r $class` );
push @TotalHosts, @hosts_per_hostclass;

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Re: splitting the scalar variables in an array
by soonix (Canon) on Nov 16, 2013 at 08:14 UTC
    I would move the split and print out of the loop.
    Update: wasn't yet awake... push @TotalHosts, split ... IN the loop, and print, of course, after the loop.
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