getting new variables into a pre-existing variable perl - perl

Question

I have a script that prints out a string of values which are pipe delimited.
waht i want to do is is if $f3 field equals something, like the letter C
I want it to print out the xout.
However if the $f3 is not populated with any value, I want N and G to be
printed out in the $f5 and F7 fileds respectively.
#!/usr/bin/perl
use strict;
use warnings;
my ( $system, $f2, $f3, $f4, $f5, $f6, $f7 ) = "";
#$f3="C";
my $xout = "$system|$f2|$f3|$f4|$f5|$f6|$f7|\n";
if ( defined $f3 && $f3 ne '' ) {
print $xout;
print "\$f3 is defined \n";
} else {
my $f5 = "N";
my $f7 = "G";
print $xout;
print "the 7th and 8th blocks should have values \n";
}
This is the output
Use of uninitialized value $f2 in concatenation (.) or string at ./test_worm_output line 6.
Use of uninitialized value $f3 in concatenation (.) or string at ./test_worm_output line 6.
Use of uninitialized value $f4 in concatenation (.) or string at ./test_worm_output line 6.
Use of uninitialized value $f5 in concatenation (.) or string at ./test_worm_output line 6.
Use of uninitialized value $f6 in concatenation (.) or string at ./test_worm_output line 6.
Use of uninitialized value $f7 in concatenation (.) or string at ./test_worm_output line 6.
|||||||
the 7th and 8th blocks should have values
If the f is uncommented I get :
(lots of uninitialized values lines)
||C|||||
$f3 is defined
what i want is if the f not defined, if is has no value I need it to print out
||||N||G|
ultimately the lines will look like this (the other fields will have values )
but if that third values is populated, I can't have the N or G and if $f3 is blank
I need the N and G.
host1||C|||||
host2||C|||||
host3||||N||G|
host4||C|||||
host5||||N||G|
thank you

Answer 1

In the line
my ($system ,$f2,$f3,$f4,$f5,$f6,$f7) = "" ;
you're only initializing the first variable in the list, $system. To initialize all of the variables in the list, you need an equal number of values on the RHS:
my ($system, $f2, $f3, $f4, $f5, $f6, $f7) = ("", "", "", "", "", "", "");
or
my ($system, $f2, $f3, $f4, $f5, $f6, $f7) = ("") x 7;
However, any time you find yourself creating numbered variables (e.g. f1, f2, f3) you should think "array" instead:
my #fields = ("") x 7;
if ($fields[2] eq "") {
#fields[4, 6] = ("N", "G");
}
print join("|", #fields), "\n";
Output:
||||N||G
(Of course, this code is rather pointless since we explicitly set $fields[2] to the empty string and then check if it's equal to...the empty string. I assume your actual code is more complex.)
In your case, it looks like the first field is distinct from the rest, so it would make more sense to store your data in a hash of arrays (assuming the hostnames are unique):
use strict;
use warnings;
# Populate the hash
my %data;
foreach my $host_num (1..5) {
my #fields = ("") x 6;
$fields[1] = "C" if $host_num == 1 or $host_num == 2 or $host_num == 4;
my $host_name = "host" . $host_num;
$data{$host_name} = [ #fields ];
}
# Print the contents
foreach my $host (sort keys %data) {
if ($data{$host}[1] eq "") {
#{ $data{$host} }[3, 5] = ("N", "G");
}
print join("|", $host, #{ $data{$host} }), "\n";
}
Output:
host1||C||||
host2||C||||
host3||||N||G
host4||C||||
host5||||N||G