not getting hostname correctly on UNIX

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

Hello Everyone! Can someone, Please, explain to me kind of weird phenomena. I have perl script below which I’m running on Sun/Solaris

Machine hardware:   sun4u
OS version:         5.8
Processor type:     sparc
Hardware:           SUNW,Sun-Fire-880
Perl version : This is perl, version 5.005_03 built for sun4-solaris
#!/bin/perl
#hostname.pl
use subs qw(getHostname LoginName HostEntry GetNetByName);
my $hostname="not defined";
print "hostname: $hostname\n";
print "*****\n";
getHostname;
print "****\n";

sub getHostname {
  #print "Hostname: ";
  system "/bin/hostname";
  #print "\n";
  #$hostname = system "/bin/hostname";
  #$hostname = exec "/bin/hostname";
  #$hostname = syscall "/bin/hostname";
  #print "Hostname: $hostname\n";
  return 0;
}
[download]

here is the output:

perl hostname.pl
hostname: not defined
*****
correct_UNIX_box_name
****
[download]

However, should I change subroutine to:

sub getHostname {
  $hostname = system "/bin/hostname";
  print "Hostname: ", $hostname, "\n";
  return 0;
}
[download]

the output will be:

perl hostname.pl
hostname: not defined
*****
correct_UNIX_box_name
Hostname: 0
****
[download]

Then in attempt to print output nicely, I made the following changes:

print "Hostname: ";
getHostname;

sub getHostname {
  system "/bin/hostname";
  return 0;
}
[download]

the output surprised me. I was under impression that Perl is a script language, which means it is being executed line by line… , so it should print out first:

Hostname:
[download]

and then on the same line:

correct_UNIX_box_name
[download]

but instead it reveres it and execute subroutine first and then print out line above. here is the output:

perl hostname.pl
hostname: not defined
*****
correct_UNIX_box_name
Hostname: ****
[download]

I don’t get it… can someone, please explain it? I’m trying to accomplish easy task: print out unix box name I’m currently in. May be someone can suggest another way to get it? The reason I inserted information about OS and UNIX machine is because I suspect it is platform dependant issue. I do not have such problem when I run the same script on Windows XP on PC - everything appears is expected.

Many Thanks in advance.

Comment on not getting hostname correctly on UNIX Select or Download Code

Replies are listed 'Best First'.
Re: not getting hostname correctly on UNIX by epoptai (Curate) on Dec 22, 2005 at 23:01 UTC
Sys::Hostname - Try every conceivable way to get hostname `-- perl -MO=Deparse -e"u j t S n a t o e h r , e p l r a h k c r e"`	[reply]
Re: not getting hostname correctly on UNIX by ikegami (Patriarch) on Dec 22, 2005 at 22:51 UTC
system doesn't do what you want. You should be using backticks: $hostname = `/bin/hostname`; [download] Also, you're needlessly using a global for a return value: sub getHostname { return `/bin/hostname`; } my $hostname = getHostname; print "hostname: $hostname\n"; [download]	[reply] [d/l] [select]
Re^2: not getting hostname correctly on UNIX by blazar (Canon) on Dec 23, 2005 at 11:36 UTC
Very valuable advice that the OP would better take into account. But since nobody has mentioned it yet, and he wrote so many lines of code for this simple task, it is also worth pointing out that he may well save himself all this trouble and use Sys::Hostname instead, which I've always found to be quite reliable.	[reply]
Re: not getting hostname correctly on UNIX by Celada (Monk) on Dec 22, 2005 at 22:54 UTC
You can also try getting the hostname without calling an external program: `perl -MPOSIX -le 'print((uname)[1])'` [download]	[reply] [d/l]
Re: not getting hostname correctly on UNIX by marto (Cardinal) on Dec 22, 2005 at 23:07 UTC
Hi slavam, I notice this is your first post (under this username). In addition to the advice given by the other monks, if you have not done so already please read the PerlMonks FAQ and How do I post a question effectively?. Using code tags when posting code make it easier for us to read your posts. Hope this helps. Martin	[reply]


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