Declare dynamic variables in bash functions

Sang -

The content of this post will be as the title suggests.

My post considers that all variables are not an array.

There are 3 ways

  • Use declare with the global flag -g. Require bash >= 4.2 or zsh
foo() {
	declare -g "my_$1"="my_$2"
}
foo var val
echo $my_var # my_val

Without -g flag, the final result will be different

foo() {
	declare "my_$1"="my_$2"
}
foo var val
echo $my_var # print nothing
  • Use eval
foo() {
	eval "my_$1=\"my_$2\""
}
foo var val
echo $my_var # my_val
  • Use printf -v
foo() {
	printf -v "my_$1" "%s" "my_$2"
}
foo var val
echo $my_var # my_val

Also, note that function calls should not be wrapped in a command substitution or any similar mechanism which introduces a new subshell. Because subshell inherits all variables from its parents and all modifications stay in the subshell environment. source