In a bash script, I have a locale in a variable like so
locale=fr_ma
I also have an associative array like this
declare -A new_loc_map
new_loc[fr_ma]=en_ma
new_loc[el_gr]=en_gr
new_loc[sl_si]=en_si
I want to check if new_loc element with the key ${locale} exists
I thought this should work but it doesn't:
if [[ -v "${new_loc[${locale}]}" ]]
then
echo -e "${locale} has a new_loc"
fi
fi
any ideas on how otherwise I can test for this?
-v takes an (indexed) name 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
While the BASH manual page describes -v for [[ and test, reliable results are returned from [[ only.
Consider this (Bash 4.4):
$ [ -v "$a[1]" ] && echo true
$ a[1]=''
$ [ -v "$a[1]" ] && echo true
$ declare -p a
declare -a a=([1]="")
$ [ -v $a[1] ] && echo true
$ [[ -v $a[1] ]] && echo true
$ [[ -v a[1] ]] && echo true
true
$ [[ -v a[0] ]] && echo true
$
On newer versions of Bash such as 5.2.37, all variations work fine, including:
$ test -v a[1] && echo true
true
$BASH_VERSION?
bash 4.3 or later for -v to work with an array index.For older verions of bash (looks like [[ -v array[index] ]] was introduced in version 4.3), you can use the ${var-word} 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
The tricky part is devising a $zz string that won't appear as actual data in your array.
Much better suggestion from @chepner:
if [[ -z "${name[$locale]+unset}" ]]; then
echo "no name for $locale"
else
echo "name for $locale is ${name[$locale]}"
fi
${name[$locale]+unset}, which will produce a non-empty string if$locale is a key, or an empty string if not.
if [[ -z "${name[$locale]+unset}" ]]; then echo "no name for $locale"; else echo "name for $locale is ${name[$locale]}"; fi
if ($h{x}) vs. if (exists($h{x})) if the element at an index may be the empty string.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 test "${new_loc[$locale]}"; then
echo "Locale ${locale} now maps to ${new_loc[$locale]}"
fi
Output:
Locale fr_ma now maps to en_ma
-n is the same as ! -z