running functions perl (basic)

[perllearner007]

Okay pardon me for this silly question (I am learning perl!) but how do we run a perl file that has many sub functions. For example, if a file called thisismyfile.pl has following sub functions

sub thisismyfunction1
sub thisismyfunction2

where sub thisismyfunction1 will output table 1 and sub thisismyfunction2 will output table 2.
then when I want to run this .pl file from command line, I write in terminal

perl thisismyfile.pl thisismyfunction1

but this doesn't seem to give me the result (as in table1) I want? Is this the way to run a perl file with various sub functions ?

[Trentacle]

Nope. If you want it to do something when you run it from the command line, you need to put code in the top level of the file (not in a function).

You can easily make your script behave this way, though, if you add the following code to it:

if ($ARGV[0] eq 'thisismyfunction1') {
    &thisismyfunction1;
} elsif ($ARGV[0] eq 'thisismyfunction2') {
    &thisismyfunction2;
}

It's simplistic and won't scale well, but it works if it's used as you describe. Depends on what you need.

[perllearner007]

Thanks Trentacle. I am noticing something, so if these are the functions:

sub thisismyfunction1()
sub thisismyfunction2()
sub thisismyfunction3()
sub thisismyfunction4()

If in my thisismyfile.pl I do the following:

&thisismyfunction1;
&thisismyfunction2; 

in the beginning of my script in the .pl file and then in terminal run it as only:

perl thisismyfile.pl

then it outputs the first two tables that sub 1 and sub 2 were coded to do. Any input on this or suggestion?
Thanks again!

[Trentacle]

Well, yeah. &sub_name; just calls the sub_name subroutine. In your example you define four subroutines and call two of them. What would you expect to happen?

[d5e5]

You could write your subroutines as values in a hash in your script and then run it from the commandline with the name of your desired function as the first argument on the command line. For example, a script named many_functions.pl

#!/usr/bin/perl
use warnings;
use strict;

my %funcs = (thisismyfunction1 => sub {print 'hello world number 1',"\n";},
             thisismyfunction2 => sub {print 'hello world number 2',"\n";},
            thisismyfunction3 => sub {print 'hello world number 3',"\n";},);

my $what_to_do = $ARGV[0];

$funcs{$what_to_do}();

Test it from the command line as follows:

david@david-laptop:~/Programming/Perl$ perl many_functions.pl thisismyfunction1
hello world number 1
david@david-laptop:~/Programming/Perl$ perl many_functions.pl thisismyfunction2
hello world number 2
david@david-laptop:~/Programming/Perl$ perl many_functions.pl thisismyfunction3
hello world number 3

You may prefer to name your subroutines, especially if they may contain lots of code, and store references to the subroutines as values in a hash. The following would give the same results as the above script:

#!/usr/bin/perl
use warnings;
use strict;

my %funcs = (thisismyfunction1 => \&world_1,
             thisismyfunction2 => \&world_2,
            thisismyfunction3 => \&world_3,);

my $what_to_do = $ARGV[0];

$funcs{$what_to_do}();

sub world_1 {print 'hello world number 1',"\n";}
sub world_2 {print 'hello world number 2',"\n";}
sub world_3 {print 'hello world number 3',"\n";}

[Trentacle]

Or

no strict 'refs';
$ARGV[0]->();

(This is not actually a recommendation, and I hereby disclaim any consequences of doing this in actual code, including but not limited to odd behavior, strange errors, problems debugging, write-only code, and enraged maintenance programmers.)

[d5e5]

I should add that experienced programmers do not require their users to memorize the real names of all their subroutines to use as command-line arguments at run-time. Make the command-line arguments short, easy to remember and spell. Use a hash or an if-elsif-else statement to associate the command-line arguments with the name of the appropriate function or subroutine. If the argument value does not correspond to any of the expected values, your script should display a warning or error message.

[perllearner007]

Thank you all for the suggestions. I am marking this as solved.