检查bash中是否存在关联数组元素

Question

In a bash script, I have a locale in a variable like so

locale=fr_ma

Answer 1

For older verions of bash ( looks like<\/a> [[ -v array[index] ]]<\/code> was introduced in version 4.3), you can use the ${var-word}<\/code> form to test is a variable has been set:

$ zz="$RANDOM$RANDOM$RANDOM"
$ echo $zz
270502100415054
$ declare -a name
$ locale=foo

$ [[ ${name[$locale]-$zz} = "$zz" ]] && echo var is unset || echo var has a value
var is unset

$ name[$locale]=""
$ [[ ${name[$locale]-$zz} = "$zz" ]] && echo var is unset || echo var has a value
var has a value

$ [[ ${name[$locale]:-$zz} = "$zz" ]] && echo var is unset or empty || echo var has a value
var is unset or empty

Answer 2

-v<\/code> takes an (indexed) name<\/em> as its argument, since you are trying to determine if the expansion makes sense in the first place.

if [[ -v new_loc[$locale] ]]; then
    echo "Locale ${locale} now maps to ${new_loc[$locale]}"
fi

Answer 3

I managed to solve the problem by checking if the variable is not an empty string instead.

Example:

locale=fr_ma
declare -A new_loc
new_loc[fr_ma]=en_ma
new_loc[el_gr]=en_gr

if [[ ! -z ${new_loc[$locale]} ]]; then
    echo "Locale ${locale} now maps to ${new_loc[$locale]}"
fi

Output:

Locale fr_ma now maps to en_ma