Passing arguments by reference

Question

I want to ask if it is possible to pass arguments to a script function by reference:

i.e. to do something that would look like this in C++:

Answer 1

#!/bin/bash

append_string()
{
if [ -z "${!1}" ]; then
eval "${1}='$2'"
else
eval "${1}='${!1}''${!3}''$2'"
fi
}

PETS=''
SEP='|'
append_string "PETS" "cat" "SEP"
echo "$PETS"
append_string "PETS" "dog" "SEP"
echo "$PETS"
append_string "PETS" "hamster" "SEP"
echo "$PETS"

Output:

cat
cat|dog
cat|dog|hamster

Structure for calling that function is:

append_string  name_of_var_to_update  string_to_add  name_of_var_containing_sep_char

Name of variable is passed to fuction about PETS and SEP while string to append is passed the usual way as value. "${!1}" refers to contents of global PETS variable. In the beginning that variable is empty and contens is added each time we call the function. Separator character can be selected as needed. "eval" starting lines update PETS variable.