Re: Strange system call failure in OS X

[karlgoethebier]

BTW, why don't you do it like this:

#!/usr/bin/env perl

use strict;
use warnings;

my $name = qq(3c0754131c6d);

my $result;

eval { $result = qx(scutil --set LocalHostName $name) };

..and then take a look $result, $?>>8 and $@?

Just an idea, don't know if this helps but best regards, Karl

[endor-moon]

Actually, this is the way I ended up doing these system calls due to its relative simplicity:

# Declare dependencies
use File::Slurp;

# Declare variables we'll be using
my $name = "";
my @args = ();
my $result = "";

# Set computer name based on MAC address of en0
my @entries = qx(ifconfig en0 | awk '/ether/ { gsub(":", ""); print \$
+2 }');
chomp(@entries);
$name = $entries[0];

[karlgoethebier]

Hi endor-moon and welcome,

After bothering myself a bit with awk (i repressed the details) i decided to take the swiss katana. I'm assuming that you just want the mac address:

#!/usr/bin/env perl                                                   
+                                            

use strict;
use warnings;

my $mac = ( split " ", ( qx(ifconfig en0) )[2] )[1];

print qq($mac\n);

__END__

Karls-Mac-mini:monks karl$ ./endor-moon.pl
2c:07:54:5e:3e:f0 # i faked this, really ;-)

This works for me. Please note also that your code didn't output anything (for me).

Btw, why do you load a module that you don't use (File::Slurp) as well as some variables (@args, $result)...or do i miss something?

My best regards, Karl

[afoken]

eval { $result = qx(scutil --set LocalHostName $name) };

• qx// is the generic form of `...`
• `...` passes a single string to the shell (except when perl is sure that a shell is not needed), so you have to handle an unknown shell with unknown behavior. Quoting is necessary to prevent shell injection, but quoting rules differ from shell to shell. See http://www.in-ulm.de/~mascheck/various/ to get an idea how different shells can behave.
• `...` does not die, eval won't catch any error in external programs, so eval is useless here.

Read the "Safe Pipe Opens" section of perlipc for a secure replacement for `...`.

The shell problem is also present in the single argument versions of system and exec, so make sure to use the multi-argument versions, which don't have this problem.

Alexander

[karlgoethebier]

Mmh...?

#!/usr/bin/env perl                                                   
+                        

eval { qx(nose --cuke) || die qq(shit: $!\n) };

print qq(Trapped this $@) if $@;

__END__

Karls-Mac-mini:monks karl$ ./nose.pl

Trapped this shit: No such file or directory

Update: I always thought that it isn't a bad idea to wrap a call to a subshell into a eval block. And i don't know what is generic with qx. It's just the same as backticks, isn't it? Just a subshell.

Regards, Karl