Calling a scalar from another script using "require"

[Regent]

Hi, friends,

Although I read several books before posting this, I still don't know how to declare a scalar in "common.pl" and use it directly in "script.pl":

common.pl

$root = "/root";


script.pl

require "common.pl"; # this line works
print "$root"; # Global symbol "$root" requires explicit package name

PS: I habitually use the -wT switch

Regent
(e-mail address removed)

 

[Gunnar Hjalmarsson]

Although I read several books before posting this,

Those cannot have been Perl books... ;-)

I still don't know how to declare a scalar in "common.pl" and use
it directly in "script.pl":

common.pl

$root = "/root";


script.pl

require "common.pl"; # this line works
print "$root"; # Global symbol "$root" requires
# explicit package name

PS: I habitually use the -wT switch

Good. Since you get that error message, you are obviously using
strictures too, which is also good.

These are two ways to do what you want:

our $root; # declares $root as a package global
require "common.pl";
print $root;

or

require "common.pl";
print $main::root; # explicit package name

(There is no need to quote the variable in the print statement.)

 

[David Efflandt]

Hi, friends,

Although I read several books before posting this, I still don't know
how to declare a scalar in "common.pl" and use it directly in
"script.pl":

Typically require inserts the contents of the required script at the point
of the require statement. However, I noticed that if I used "my $root",
it only seemed to be in scope in the required script, and was
uninitialized in main script.

common.pl

$root = "/root";


script.pl

require "common.pl"; # this line works
print "$root"; # Global symbol "$root" requires explicit package name

PS: I habitually use the -wT switch

Regent
(e-mail address removed)

If I just used -w switch (and put a newline in print "$root\n",
I got:

Name "main::root" used only once: possible typo at ./mytest line 3.
/root

Inserting a use vars line got rid of the warning:

use vars ('$root');
require "common.pl";
print "$root\n"

If I used -wT, "." (current dir) was apparently excluded from @INC, so I
had to use a full path to common.pl (same output).

Tested in perl v5.6.1 built for i586-linux and v5.8.0 built for
i586-linux-thread-multi

 

[Tad McClellan]

However, I noticed that if I used "my $root",
it only seemed to be in scope in the required script, and was
uninitialized in main script.

That is what my() is _supposed to do.


perldoc -f my

... local (lexically) to the enclosing block, file ...


$root will only be in the scope of the "required file" since
my() variables can never cross file boundaries.

 

[Regent]

---------------------

Those cannot have been Perl books... ;-)

Well, those were books ABOUT Perl. The Perl books (to which I believe you refer) seem to discuss principles rather than specific problems, but I'm not much more than a newbie (

These are two ways to do what you want:

our $root; # declares $root as a package global

You mean in common.pl? I put this line in common.pl, but it seemed I had also to declare $root in script.pl, otherwise I still got a "Global symbol "$root" requires explicit package name" error. Then I tried "my $root;" in script.pl, but got a "Use of uninitialized value", though I had already expected this error msg. The problem seems to be how do declare $root AGAIN in script.pl, which sounds weird to me

require "common.pl";
print $root;

or

require "common.pl";
print $main::root; # explicit package name

This worked! Thanks indeed, but what does $main here mean? "::" means the use of modules to me. BTW, $main::root appears to be a somewhat clumsy

(There is no need to quote the variable in the print statement.)

Regent
(e-mail address removed)

 

[Gunnar Hjalmarsson]

You mean in common.pl?

No, I mean in script.pl. Both my suggestions were intended for
script.pl, while keeping common.pl as it is.

This worked! Thanks indeed, but what does $main here mean?

$main::root means the global variable $root in package main.

"::" means the use of modules to me.

When something begins with a '$' character, it's most likely a
variable. You'd better do some reading:

http://www.perldoc.com/perl5.8.0/pod/perlmod.html

 

[Regent]

------------------------

No, I mean in script.pl. Both my suggestions were intended for
script.pl, while keeping common.pl as it is.

Okay, I see. If I use this method, I must declare all scalars in script.pl like this, right?

$main::root means the global variable $root in package main.


When something begins with a '$' character, it's most likely a
variable. You'd better do some reading:

Yup, I know the '$' well, but never used "::" in this way

 

[Gunnar Hjalmarsson]

Okay, I see. If I use this method, I must declare all scalars in
script.pl like this, right?

Only those scalars you require from other files that way. Other
variables should preferrably be declared with my().

 

[Regent]

------------------------

If I just used -w switch (and put a newline in print "$root\n",
I got:

Name "main::root" used only once: possible typo at ./mytest line 3.
/root

Inserting a use vars line got rid of the warning:

use vars ('$root');
require "common.pl";
print "$root\n"

If I used -wT, "." (current dir) was apparently excluded from @INC, so I
had to use a full path to common.pl (same output).

Yeah, this is a problem. If common.pl isn't in one of the paths already indicated in @INC, I must specify its full path in every script, right?

 

[Jason Hood]

or you can include it in the @INC path

use lib('PATH','ANOTHERPATH');

J