How can I execute Perl code specified on the command line?

Question

I want something like..

all_objects.pl

my $sub = $ARGV[1];
...

@objs = get_all_objects();
for my $obj (@objs) {
    // invoke subroutine $sub with param as $obj.   
}

now if I say

all_objects.pl "print 'x '" 

all_objects.pl "print '$_ '"

I should get

obj1 obj2 obj3 ...

i.e. the command line arg act as a subroutine in some way. Can this be achieved?

Answer 1

Eval is evil unless you really know what you're doing (think of it as an unshielded thermonuclear nuke -- sure you could handle one if you had to, and it might even save the world, but you'd be better off leaving it as a last resort, and let the nuclear physicists deal with it.)

You could put your all_objects.pl code into a module, and then use the module on the command line:

put this into AllObjects.pm:

package AllObjects;
use strict;
use warnings;

sub get_all_objects
{
    # code here...
}
1;

Now on the command line:

perl -I. -MAllObjects -wle'for my $obj (AllObjects::get_all_objects()) { print "object is $obj" }'

However, it's not really clear what you are trying to achieve with the overall design.

You can read more about perl command-line invokation at perldoc perlrun, and making modules at perldoc perlmod (as well as many posts here on Stack Overflow).

Answer 2

eval "" is bad. Use something like the following, if it fulfills your needs:

my ($sub) = @ARGV;

my %prepared = (
    print => sub { print "$_[0]\n" },
    woof  => sub { $_[0]->woof },
    meow  => sub { $_[0]->meow },
);

@objs = get_all_objects();
for my $obj (@objs) {
    $prepared{$sub}->($obj);   
}

Update: For debugging purposes, Perl has a debugger: perldoc perldebug