Sharing variables between shell scripts

Question

I have a shell script (let's call it parent.sh) which calls another shell script (child.sh), passing it an argument.

The child script does some work and sets a value in a variable called create_sql. I want to access this create_sql variable from the parent script which invoked it.

I am calling the child script from within the parent script like this:

./child.sh "$dictionary"

and straight afterwards I have the line:

echo "The resulting create script is: "$create_sql

However, there is no value being output, however, in the child script I am doing the same thing and the variable is definitely set.

How can I get this to work so that I can read variables created by the child script?

Answer 1

Succinctly, you can't have a child script set a variable in the parent script unless you do something like:

. ./child.sh "$dictionary"

(or in Bash, mimicking the C shell, source ./child.sh "$dictionary"). This reads and executes the script in the environment of the current shell, but could alter any other variable in the parent.sh script; there is no isolation between the scripts. Otherwise, a child process cannot sanely set the environment of the parent shell. (If you want to do it insanely, you can have the child shell run a debugger, attach to the parent shell process and set the environment that way — but calling it 'insane' is being polite).

Arguably, the best way to get output from the child stashed in a variable in the parent script is to have child.sh echo the value you want in $create_sql, and then you use

create_sql=$(./child.sh "$dictionary")
echo "The resulting create script is: $create_sql"

with no spaces around the assignment operator. Note that the echo includes the variable inside the double quotes; this will preserve internal spacing (including newlines) in the variable's value. As written in the question, the variable is flattened into a space-separated stream of 'words' (sequences of non-spaces), losing any internal spacing.

Answer 2

Use the source Luke ! source word ( or . ) allows to run a script like if it was in current shell. beware, your script and the source one are 'married' :-) , sourced script have full access to all variables for the better or the worse...

Other ways implies to modify called script to put is result in a stream format that will be read by caller using script params | read VAR or RESULT=$(SCRIPT params) and echoing results from your called script