Return variable value from a script running in background

Shell Programming and Scripting
1

I have a script which runs a script in the background. Now the script running in background returns some variable value and i want to catch return value in the parent script.

e.g.
Parent Script :

#!/bin/bash
./Back.sh &
pid=$!
echo "a=$a"
echo "b=$b"
echo "d=$((a+b))"
wait $pid

Child Script run in background

a=4
b=5
c=6

Now when i run ./BackGroundProcess.sh , expected output is :
a=4
b=5
d=9

what i get is
a=
b=
d=0

Any suggestions or approach how I can retrieve a variable value from a script running in background ?

2

Hi,

Check this http://www.unix.com/shell-programming-scripting/89117-how-export-variable-child-process-running-background-parent.html

Cheers,
Ranga:)

3

Thanks rangarasan. :confused:

4

A child script cannot pass variables to a parent script. There are ways to read the output of the child script in the parent script. For example:

$ cat back.sh
echo 4 5

$ cat fore.sh
TESTFIFO=./testfifo
mkfifo "$TESTFIFO"
./back.sh > "$TESTFIFO" &
echo hello
read a b < "$TESTFIFO"
echo "a=$a"
echo "b=$b"
echo "d=$((a+b))"
rm "$TESTFIFO"

$ ./fore.sh
hello
a=4
b=5
d=9

Alternatively, ksh93 and bash 4 can use coprocesses

5

Thanks dude.

Though I already tried this approach by redirecting output to TEMP.sh from the script running in background and then calling ./TEMP.sh from the script running in forground.

Though thanks for your input. :cool::stuck_out_tongue:

TR,
Shaishav