I think we are in different pages here.
I understand (at least sometimes) the need not to use anything outside perl core modules.
But my suggestion was for you to make (not install! -- no root access needed) your own modules. It's basically the same thing as making another ".pl" file, but with many, many advantages (no namespace pollution, etc).
So, I'll repeat what I think you should do: instead of making a file called complex_calculation.pl, make a file called ComplexCalculation.pm, with the following contents:

use strict;
package ComplexCalculation;
sub do_calc {
  # put your calculation here.
  return 4 + 8 * 15 / 16 - 23 * 42;
}
1;
[download]

Now, in your scripts, everywhere where you had require 'complex_calculation.pl' (*), you will put:

$variable1 = ComplexCalculation::do_calc();
[download]

And, at the top of those scripts, you will put:

use ComplexCalculation;
[download]

I am assuming that ComplexCalculation.pm and your scripts are in the same directory. Otherwise, before the use line above, you have to put:

use lib '/some/path/to/the/calc/module';
[download]

(just the dir).
(*) Anyway, this would NOT work unless the require line was used only once each script, because require does not read the same file again, when it alredy did.
In another note, always use strict; use warnings; ...

---

Update:
You can still assign to multiple variables (even if you use only one calculation to figure them all) -- in ComplexCalculation.pm:

sub do_calc {
  my $v1 = ##... something
  my $v2 = ##... other thing
  my $v3 = ##... a third thing
  return $v1, $v2, $v3
}
[download]

and in your scripts:

my ($r1, $r2, $r3) = ComplexCalculation::do_calc()
[download]

Notice that each of your scripts may use its own relevant name for each variable, and they can even ignore one or more results:

my ($weight, undef, $depth) = ComplexCalculation::do_calc()
[download]