Bad array subscript error when trying to increment an associative array element

Question

I can create an associative array and assign an integer to a key that contains a single quote in it:

Answer 1

The single quote in key name is causing the parser to treat it as a un-terminated quote character. One way to fix this would be to escape the ' character in the key

key="john's"
printf -v escKey "%q" "$key"

now because of the %q specifier, printf() would have applied required escapes to all shell meta characters i.e. making it "shell-quoted" and re-usable. If you print the contents of escKey you'll notice the ' escaped

printf '%s\n' "$escKey"
john\'s

Now you can use this keyname in your associative array. Remember you can always manually add the escapes which could be messy. Since %q is a native way provided by the shell, it is much safe to use it.

(( dict["$escKey"]++ ))

Also in bash versions >= 4.4 parameter expansion has @Q which is a shortcut for %q specifier of printf() using which you can do

(( dict["${key@Q}"]++ ))

Answer 2

Turn off multiple evaluation^* of associative array subscripts with following command and it'll work.

shopt -s assoc_expand_once

^* An example showing the default behavior and assoc_expand_once's effect:

$ v1=42
$ v2='$v1'
$ declare -A foo
$ foo[$v2]=
$ declare -p foo
declare -A foo=(["\$v1"]="" )
$ (( foo[$v2]++ ))
$ declare -p foo
declare -A foo=([42]="1" ["\$v1"]="" )
$
$ shopt -s assoc_expand_once
$ (( foo[$v2]++ ))
$ declare -p foo
declare -A foo=([42]="1" ["\$v1"]="1" )