modification of passed in array

You may have good reasons to do that but when I'm faced with similar situations I wonder if returning a new version of the array might be better/safer.

#! /usr/perl/bin

use warnings;
use strict;
use Data::Dumper;

sub process_array_ref { 

  my $initial_array_ref = shift;
  my @processed_array;

  for my $element (@{$initial_array_ref}){

    # do something with element
    # validate, normalise, error checking,
    # convert to metric, skip, whatever

    push @processed_array, sprintf(qq{processed: %s}, $element);
  
  }

  return \@processed_array;

}

my $initial_array_ref     = ['a','b','c','d','e'];
my $processed_array_ref   = process_array_ref($initial_array_ref);

print Dumper($processed_array_ref);
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I often find that debugging/maintainance is easier with this approach. YMMV.