New answer
From version 4.2 of bash (and newer), there is a new -v option to built-in test command.
From version 4.3, this test could address element of arrays.
array=([12]="red" [51]="black" [129]="blue")
for i in 10 12 30 {50..52} {128..131};do
if [ -v 'array[i]' ];then
echo "Variable 'array[$i]' is defined"
else
echo "Variable 'array[$i]' not exist"
fi
done
Variable 'array[10]' not exist
Variable 'array[12]' is defined
Variable 'array[30]' not exist
Variable 'array[50]' not exist
Variable 'array[51]' is defined
Variable 'array[52]' not exist
Variable 'array[128]' not exist
Variable 'array[129]' is defined
Variable 'array[130]' not exist
Variable 'array[131]' not exist
Note: regarding ssc's comment, I've single quoted 'array[i]' in -v test, in order to satisfy shellcheck's error SC2208. This seem not really required here, because there is no glob character in array[i], anyway...
This work with associative arrays in same way:
declare -A aArray=([foo]="bar" [bar]="baz" [baz]=$'Hello world\041')
for i in alpha bar baz dummy foo test;do
if [ -v 'aArray[$i]' ];then
echo "Variable 'aArray[$i]' is defined"
else
echo "Variable 'aArray[$i]' not exist"
fi
done
Variable 'aArray[alpha]' not exist
Variable 'aArray[bar]' is defined
Variable 'aArray[baz]' is defined
Variable 'aArray[dummy]' not exist
Variable 'aArray[foo]' is defined
Variable 'aArray[test]' not exist
With a little difference:
In regular arrays, variable between brackets ([i]) is integer, so dollar symbol ($) is not required, but for associative array, as key is a word, $ is required ([$i])!
Old answer for bash prior to V4.2
Unfortunately, bash give no way to make difference betwen empty and undefined variable.
But there is some ways:
$ array=()
$ array[12]="red"
$ array[51]="black"
$ array[129]="blue"
$ echo ${array[@]}
red black blue
$ echo ${!array[@]}
12 51 129
$ echo "${#array[@]}"
3
$ printf "%s\n" ${!array[@]}|grep -q ^51$ && echo 51 exist
51 exist
$ printf "%s\n" ${!array[@]}|grep -q ^52$ && echo 52 exist
(give no answer)
And for associative array, you could use the same:
$ unset array
$ declare -A array
$ array["key1"]="red"
$ array["key2"]="black"
$ array["key3"]="blue"
$ echo ${array[@]}
blue black red
$ echo ${!array[@]}
key3 key2 key1
$ echo ${#array[@]}
3
$ set | grep ^array=
array=([key3]="blue" [key2]="black" [key1]="red" )
$ printf "%s\n" ${!array[@]}|grep -q ^key2$ && echo key2 exist || echo key2 not exist
key2 exist
$ printf "%s\n" ${!array[@]}|grep -q ^key5$ && echo key5 exist || echo key5 not exist
key5 not exist
You could do the job without the need of externals tools (no printf|grep as pure bash), and why not, build checkIfExist() as a new bash function:
$ checkIfExist() {
eval 'local keys=${!'$1'[@]}';
eval "case '$2' in
${keys// /|}) return 0 ;;
* ) return 1 ;;
esac";
}
$ checkIfExist array key2 && echo exist || echo don\'t
exist
$ checkIfExist array key5 && echo exist || echo don\'t
don't
or even create a new getIfExist bash function that return the desired value and exit with false result-code if desired value not exist:
$ getIfExist() {
eval 'local keys=${!'$1'[@]}';
eval "case '$2' in
${keys// /|}) echo \${$1[$2]};return 0 ;;
* ) return 1 ;;
esac";
}
$ getIfExist array key1
red
$ echo $?
0
$ # now with an empty defined value
$ array["key4"]=""
$ getIfExist array key4
$ echo $?
0
$ getIfExist array key5
$ echo $?
1
