why main() call automatically?

Thai Heng has asked for the wisdom of the Perl Monks concerning the following question:

I am learning Modern Perl. The perl file chapter5_2.pl have code :

#!/bin/perl
use v5.14.2;
use strict;
use Carp;


package main;

main();

sub main
{
    show_call_information();
}

sub show_call_information
{
    my ($package, $file, $line,$func) = caller(0);
    say "Called $func from $package in $file:$line";
}

say "---------use Carp------------------";

say add_numbers(1,2,3);

sub add_numbers
{
    croak 'Expected two numbers, received:' . @_
    unless @_ == 2;
    my ($one, $two) = @_;
    return $one + $two;
}
[download]

I run as

   perl chapter5_2.pl
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get the following output:

 Called main::show_call_information from main in chapter5_2.pl:13
---------use Carp------------------
Expected two numbers, received:3 at chapter5_2.pl line 28.
    main::add_numbers(1, 2, 3) called at chapter5_2.pl line 24
[download]

I can't know why the main() function is called automatically? What's the mechanism?

How can I get result from formal document such as perldoc?

Thanks!

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Re: why main() call automatically? by kcott (Archbishop) on Jan 17, 2014 at 01:58 UTC
G'day Thai Heng, I suspect you may be confusing the `main` in `main::show_call_information` (which is a package and documented in package and perlmod: Packages) with `main` in `main()` and `sub main {...}` (which is a subroutine and documented in perlintro: Basic syntax overview and perlintro: Writing subroutines). [Note: many of the pages I've linked to contain links to further, relevant information.] `main::show_call_information` indicates the `show_call_information` subroutine in the `main` package; it is not providing information that `show_call_information()` was called from `main()`. If that still seems confusing, try changing the name of the `main` subroutine to something unambiguous: the new output should probably prove enlightening. You may also find these fairly recent threads to be of interest: "creating a perl entry-point" and "Main routines, unit tests, and sugar". -- Ken	[reply] [d/l] [select]
Re: why main() call automatically? by Anonymous Monk on Jan 16, 2014 at 23:56 UTC
I can't know why the main() function is called automatically? What's the mechanism? It isn't called automatically. The line `main();` calls the main function How can I get result from formal document such as perldoc? What do you mean by that, what result? ?? `my $std_output = qx{perldoc perldoc };`	[reply] [d/l]
Re: why main() call automatically? by bulk88 (Priest) on Jan 17, 2014 at 05:13 UTC
First learn Perl, then learn Modern Perl. Modern Perl is a coding policy, not a language.	[reply]
Re^2: why main() call automatically? by chromatic (Archbishop) on Jan 17, 2014 at 18:14 UTC
How is that helpful?	[reply]
Re^2: why main() call automatically? by Anonymous Monk on Jan 21, 2014 at 04:17 UTC
bulk88 says: First learn Perl, then learn Modern Perl. Modern Perl is a coding policy, not a language. Modern Perl is the book the code sample originally came from	[reply]
Re: why main() call automatically? by Thai Heng (Beadle) on Jan 21, 2014 at 00:34 UTC
Now I get it. `main::add_numbers(1, 2, 3) called at chapter5_2.pl line 24` This is not show_call_information() function output, So there is no automatically called.	[reply] [d/l]