In bash shell for variables:

#!/bin/bash
set -o nounset

my_var=aaa
unset var
echo "$var"

Because set command is defined to return error if variable is not set, last line returns error:

line 6: var: unbound variable

OK, that is what I want.

Now the same thing with arrays:

#!/bin/bash
set -o nounset

my_array=(aaa bbb)
unset my_array
echo "${my_array[@]}"

But to my surprise last line does not return error. I would like bash script to return error when array is not defined.

CodePudding user response：

${my_array[@]} is similar to $@ which is documented to be ignored by nounset:

-u Treat unset variables and parameters other than the special parameters "@" and "*" as an error when performing parameter expansion. If expansion is attempted on an unset variable or parameter, the shell prints an error message, and, if not interactive, exits with a non-zero status.

Returning the array size is not ignored, though. Prepend the following line to make sure the array is not unset:

: ${#my_array[@]}