If I really had no other choice than to do this, I wouldn't embed the password in the main script.

I'd tuck it away in a module, probably one of the system module ( and include several that aren't required ), and export the password into the main namespace.

I'd probably tie the variable and only return the correct password after a particular value has been assigned to it.

And I'd only return the correct password once.

Thereafter, I would return the value passed.

In the script it would look like this:

#! perl
use strict; 
use warnings;
use diagnostics;
use LWP;
use This;
use That;
use The::Other;

our $password = 'mysecret';

....

system( "command -p $password" );

...
## If you print $password here, you get "mysecret";
## But for the first time it was FETCH'd ONLY, 
## it would be different.
[download]

Of course, now I've told you this, I'll have to kill you so that you can't tell anyone else.