How can I use "member" variables of a module inside a function? - perl

Question

I have this code:
#!/usr/bin/perl
package Modules::TextStuff;
use strict;
use warnings;
use Exporter;
our #ISA = qw(Exporter);
our #EXPORT = qw(get_text);
my $author;
my $text_tmp1 =<<'ENG';
This is a template text
by $author.
ENG
sub get_text {
my $tmp = shift #_;
$author = shift #_;
print "In sub author= $author lang = $tmp \n";
my $final_str = eval('$text_'.$tmp);
print "$final_str \n";
return $final_str;
}
1;
Test script:
#!/usr/bin/perl
use strict;
use warnings;
use Modules::TextStuff;
my $str = get_text('tmp1','jim');
print $str;
When I run the test script it does not work. I get:
In sub author=jim lang = eng
Variable "$text_tmp1" is not available at (eval 1) line 2. Use of
uninitialized value $final_str in concatenation (.) or string
How can I fix this?

Answer 1

Combining strings to create variables names is usually a bad idea. You could salvage your current program using our $text_tmp1 = ... instead of my $text_tmp1 = ..., but I think you should consider a different approach, like a hash:
my %templates = (
tmp1 => <<ENG,
This is a template text
by \$author.
ENG
tmp2 => <<ESP,
Esta es templata texta de \$author.
ESP
);
sub get_text {
...
my $final_str = eval( $templates{$tmp} );
...
}

Answer 2

The error you asked about is generated when eval EXPR tries to grab the value of a variable that did exist, but no longer exists.
>perl -wE"{ my $x = 123; sub f { eval '$x' } } say '<'.f().'>';"
Variable "$x" is not available at (eval 1) line 2.
Use of uninitialized value in concatenation (.) or string at -e line 1.
<>
Remember, executing a file (such as a script or a module) is done in its own a lexical scope, just like the one the curlies create above.
It can be fixed by keeping the variable alive by not letting it go out of scope
>perl -wE"my $x = 123; sub f { eval '$x' } say '<'.f().'>';"
<123>
But that's not an option for you.
Other options include making the variable a global variable.
>perl -wE"{ our $x = 123; sub f { eval '$x' } } say '<'.f().'>';"
<123>
Or forcing the sub to capture it so it doesn't cease to exist.
>perl -wE"{ my $x = 123; sub f { $x if 0; eval '$x' } } say '<'.f().'>';"
<123>
(The if 0 silences the "void context" warning.)
That said, it looks like you're trying to re-invent the wheel. Don't invent another half-assed templating system.

Answer 3

I'm looking at several things:
First of all, $text_tmp1 is not a package variable. It's lexically scoped since you declared it with my. If you need it as a package variable and for it to be visible in all or your subroutines, you need to declare it with our.
Your module doesn't compile as written. You are trying to source in $author, but it's not defined.
What are you doing with eval? This is wrong on so many levels.
Here's how I would do it:
#! /usr/bin/env perl
package Modules::TextStuff;
use strict;
use warnings;
use Exporter qw(import);
use Carp;
our #EXPORT_OK = qw(get_text);
our %templates; # This is now a package variable
#
# TEMPLATES
#
$templates{tmp1}=<<TEMPLATE; # We'll use `%s` for replacements
This is a template text
by %s.
TEMPLATE
$templates{tmp2}=<<TEMPLATE;
This is another template and we will substitute
in %s in this one too.
TEMPLATE
sub get_text {
my $template = shift;
my $author = shift;
if ( not exists $templates{$template} ) {
croak qq(Invalid template name "$template");
}
return sprintf $templates{$template}, $author;
}
1;
I'll make each of these templates an entry in my %templates hash. No need for eval to calculate out a variable name for the template. Also notice that I can now actually test whether the user passed in a valid template or not with the exists.
Also note that %template is declared with our and not my. This makes it available in the entire package including any subroutines in my package.
I also use #EXPORT_OK instead of #EXPORT. It's considered more polite. You're requesting permission to pollute the user's namespace. It's like knocking on someone's door and asking if you can have a beer rather than barging in and rummaging through their fridge for a beer.
Note how I use sprintf to handle the replaceable parameters. This again removes the need for eval.
I also prefer to use #! /usr/bin/env perl on my program header since it's more compatible with things like Perlbrew. You're using /usr/bin/env to find the executable Perl program that's in the user's path. This way, you don't have to know whether it's /bin/perl, /usr/bin/perl, /usr/local/bin/perl, or $HOME/perl5/perlbrew/perls/perl-5.18.0/bin/perl
To use your module, I would do this:
#! /usr/bin/env perl
use strict;
use warnings;
use feature qw(say);
use Modules::TextStuff qw(get_text);
say get_text('tmp1','jim');
Pretty much the same call you made. This prints out:
This is a template text
by jim.