How to Force String Type on a Variable?

Question

I have this script:

#!/bin/bash
USERS=("user1.com" "user2.co.uk" "user3.com")
PASSES=("pass1" "pass2" "pass3")

for i in ${USERS[@]}; do
    echo ${PASSES[i]};
done

running this script outputs:

my-script.sh: line 6: user1.com: syntax error: invalid arithmetic operator (error token is ".com")

However, my values are wrapped in quotes and as far as I know, echo isn't an arithmetic operation.

Coming from a PHP background, this is confusing. In PHP we can do:

echo gettype($string);
echo gettype($int);

which outputs

string
integer

Yet, the quotes seemingly do not do as I'd think. How do I force string usage instead of treating user1.com as user1 . com?

Answer 1

Your current code expands to

for i in user1.com user2.co.uk user3.com; do
    echo ${PASSES[i]};
done

which of course makes no sense at all. The indirection operator produces a list of array indices instead:

bash$ echo "${!USERS[@]}"
0 1 2

So with that, you can loop over the individual indices. Let's also add correct quoting.

for i in ${!USERS[@]}; do
    echo "${PASSES[i]}"
done

For full points, you should not use upper case for your private variables; uppercase variable names are reserved for system use.