Question

So, I got a PERL script I am trying to run, it start like this:

use strict;
use a;

use CGI 'param';
use URI::Escape;
use HTML::FromText 'text2html';
use XML::Simple;
use LWP::UserAgent;
use Data::Dumper;
use URI::Escape;
use DBI;
use Tie::DBI;
use Digest::MD5 'md5_hex';
use MIME::Base64;
use Encode;

my $r = shift; $r->content_type("text/html; charset=utf-8"); my $tmp = a::tmp();

When it get’s to the part where content_type() function is called, it fails with this error message:

Can't call method "content_type" on an undefined value at script.pl line 18.

Any ideas? I am kinda PERL newbie.

Answer 1

If $r is coming from @ARGV, it won’t have a content_type method.

You could potentially bless $r into some package, but that’s surely not what you’re intending to do, here.

I’m guessing that you want to obtain a CGI parameter, probably a POSTed upload file? So you want $r to be a CGI object, not a parameter. You’d start with

 my $r = CGI->new;

But, then, I refer you to the very fine manual for CGI, http://perldoc.perl.org/CGI.html or perldoc CGI from the shell.

(To expand a bit:)

In Perl, a $scalar var holds “any one thing.” Things coming in from the command-line are generally strings (maybe numbers, on a good day); that’s what shift would get at the top level. (The special variable @ARGV contains command-line parameters passed in to your program.)

“One thing” can also be a reference to an object. In Perl’s Object Oriented model, the methods of a package (“class”) are tied to that reference using bless. That’s usually handled for you, though; the special subroutine (aka function, method) CGI::new will create a new CGI object with some state data (things like form fields’ values), and bless it into the CGI package.

The -> notation going to a function call will only work if your variable contains a blessed reference. You can “ask” what kind of a reference you have in a variable using ref; you’ll get the name of its package (aka class). ($foo = []; bless $foo => 'Some::Package'; print ref $foo; => Some::Package)

— But, again, for your specific case, check out some of the examples in the CGI module’s manual 🙂