In Bash test if associative array is declared
associative-array, bash
Solution
In `bash` 4.3 or later, you can use the `-v` option:
[[ -v FOO[@] ]] && echo "FOO set"
Note that in any version, using
declare -A FOO
doesn't actually create an associative array immediately; it just sets an attribute on the name `FOO` which allows you to assign to the name as an associative array. The array itself doesn't exist until the first assignment.
Problem
How can I test if an associative array is declared in Bash? I can test for a variable like: ``` [ -z $FOO ] && echo nope ``` but I doesn't seem to work for associative arrays: ``` $ unset FOO $ declare -A FOO $ [ -z $FOO ] && echo nope nope $ FOO=([1]=foo) $ [ -z $FOO ] && echo nope nope $ echo ${FOO[@]} foo ``` EDIT: Thank you for your answers, both seem to work so I let the speed decide: ``` $ cat test1.sh #!/bin/bash for i in {1..100000}; do size=${#array[@]} [ "$size" -lt 1 ] && : done $ time bash test1.sh #best of five real 0m1.377s user 0m1.357s sys 0m0.020s ``` and the other: ``` $ cat test2.sh #!/bin/bash for i in {1..100000}; do declare -p FOO >/dev/null 2>&1 && : done $ time bash test2.sh #again, the best of five real 0m2.214s user 0m1.587s sys 0m0.617s ``` EDIT 2: Let's speed compare Chepner's solution against the previous ones: ``` #!/bin/bash for i in {1..100000}; do [[ -v FOO[@] ]] && : done $ time bash test3.sh #again, the best of five real 0m0.409s user 0m0.383s sys 0m0.023s ``` Well that was fast. Thanks again, guys.