[shell] How to store an output of shell script to a variable in Unix?

i have a shell script "script.sh" which gives output as "success" or "Failed" when i execute in unix window. Now i want to store the output of script.sh into a unix command variable. say $a = {output of script.sh}

Suppose you want to store the result of an echo command

echo hello   
x=$(echo hello)  
echo "$x",world!  

output:

hello  
hello,world!

You need to start the script with a preceding dot, this will put the exported variables in the current environment.

#!/bin/bash
...
export output="SUCCESS"

Then execute it like so

chmod +x /tmp/test.sh
. /tmp/test.sh

When you need the entire output and not just a single value, just put the output in a variable like the other answers indicate

You should probably re-write the script to return a value rather than output it. Instead of:

a=$( script.sh ) # Now a is a string, either "success" or "Failed"
case "$a" in
   success) echo script succeeded;;
   Failed) echo script failed;;
esac

you would be able to do:

if script.sh > /dev/null; then
    echo script succeeded
else
    echo script failed
fi

It is much simpler for other programs to work with you script if they do not have to parse the output. This is a simple change to make. Just exit 0 instead of printing success, and exit 1 instead of printing Failed. Of course, you can also print those values as well as exiting with a reasonable return value, so that wrapper scripts have flexibility in how they work with the script.

export a=$(script.sh)

Hope this helps. Note there are no spaces between variable and =. To echo the output

echo $a