Shell Programming and Scripting

I'm having a spot of trouble. I'm trying to test three variables for a NULL value in a bash shell script. If a null value is detected in the variable to set it to set the variable to a default value.


here is what I have:

testResponseA=3
testResponseB=
testResponseC=4

for test in "$testResponseA" "$testResponseB" "$testResponseC"; do
echo loop start checking $test
if [ "$test" = "" ]; then
test=999
echo $test

fi
echo loop end
done

echo $testResponseA
echo $testResponseB
echo $testResponseC


I realize that the test is being set and testResponseB is not getting the new value. How do I set the variable with the null value to the default value?

Code:

: ${testResponseA:=defaultA} ${testResponseB:=defaultB} ${testResponseC:-defaultC}

echo $testResponseA
echo $testResponseB
echo $testResponseC

I don't quite understand. How does this replace the null value in testResponseB without resetting testResponseA of testResponseC?

Read the Parameter Expansion section of the bash man page:

Code:

   ${parameter:=word}
       Assign Default Values. If parameter is unset or null,
       the expansion of word is assigned to parameter. The
       value of parameter is then substituted. Positional
       parameters and special parameters may not be assigned to
       in this way.

Thanks, that seems to have done it.

CFAJ's given the best response, but as an exercise here's the answer to the question as you posed it:

Code:

[rick@kangaroo ~]$ cat test.sh
#!/bin/bash

testResponseA=3
testResponseB=
testResponseC=4

for t in testResponseA testResponseB testResponseC
do
echo loop start checking $t

if [[ "${!t}" -eq "" ]]
then
eval $t=999
fi
echo loop end
done

echo $testResponseA
echo $testResponseB
echo $testResponseC
[rick@kangaroo ~]$ ./test.sh
loop start checking testResponseA
loop end
loop start checking testResponseB
loop end
loop start checking testResponseC
loop end
3
999
4
[rick@kangaroo ~]$