Quick perl question

[bigshooter]

here's some quick perl code that I wrote, and I'm wondering why it's giving me errors.
I want to exit the program and output a mesage if there are no command line arguments to this program so i just use

if (!@argv)
{
print "useage $0: command line args;
exit (1);
}

and yes i know i could use die instead, but i'm too used to c++. my problem is when I add this to my code, it gives me this

Global symbol "@argv" requires explicit package name at prog11.pl line 21.
Execution of prog11.pl aborted due to compilation errors (#1)
Uncaught exception from user code:
Global symbol "@argv" requires explicit package name at prog11.pl line 21.
Execution of prog11.pl aborted due to compilation errors.

i'm just curious why you can access elements of @argv, or do something like $temp = shift ...which uses @argv as default,
but you can't say if argv is empty kill the prog. Anyone that is a little more advanced with perl than I am know this answer? Also, any other better ways to check for arguments?

Thanks.

 

[Descartes]

It's ARGV. You need to use the array in a scalar context to get the upper bound...

if (!scalar(@ARGV)) {
# usage...
}

if ($#ARGV == -1) {
# usage...
}

If you simply want to process arguments, there are easier ways:

use Getopt::Long;
my $filename= '';

GetOptions('filename=s' => \$filename);

Lookup Getopt and friends in the docs.

 

[stndn]

if you want simple command line argument checking (ie: pre-determined usage of arguments, where script.pl -ln != script.pl -n -l), you can simply use the contents of @ARGV, with the first argument in $ARGV[0];

if you want complicated command line argument processing (ie: script.pl -ln == script.pl -n -l), you will need to
use Getopt::Std;
die "\n" if !getopts("ln", \%opts);

more info on Getopt::Std

 

[bigshooter]

i was just going to use

if (!$argv[0])

but I was curious why you couldn't use @argv in an expression like that. If you declare an array, my @temp, then you can say if (!@temp). Is the !@argv line not working because its a default variable, or does it have something to do with global scope, or is it just something that doesn't work?

 

[stndn]

you almost got that right, but remember perl in case sensitive
@ARGV (capital letters) is the default list/array to store the command line arguments entered by user
@argv is something you can create and use later if you want to ... has nothing to do with CLA

 

[bigshooter]

HAHAHAHAHAHAHHAHAHHA.

God i'm an idiot. I rely on default variables too much, the extent of my perl coding has been just shifting elements of ARGV like

$temp = shift.

I completely forgot that its ARGV, not argv. The first guy posting tried to tell me that I think, I just didn't pay attention. I thought I was really getting the hang of this perl stuff, oh well.. I should have caught that.

Thanks.