returning boolean from function ?

cmosentine · 02-16-2012, 08:18 AM

Hi all: Being new to BASH scripting, I am having a hard time getting my head around boolean usage. Below is some code that does not work properly. Looking at various online docs, it appears to me that this should work, but does not.

Thanks, Chris.

Code:

function get_host_file_list {
#do something in here

if [ #test results of above ]; then
	return 0  #true
else
	return 1  #false
fi
}

results=get_host_file_list(#parameters in here)
if [ $results ]; then
       #the if statement is always returning true
else
       #never gets here
fi

catkin · 02-16-2012, 08:50 AM

bash functions do not return values, they only set $? Thus

Code:

results=get_host_file_list(#parameters in here)

should return a syntax error.

How about

Code:

get_host_file_list(#parameters in here)
if [[ $? -eq 0 ]]; then
    echo "get_host_file_list returned 0"
else
    echo "get_host_file_list returned non-0"
fi

cmosentine · 02-16-2012, 09:05 AM

Thanks for the reply. I used your suggestion but changed it a bit to make it easier to read (for me that is). In my function I echo back a 1 or 0 and store it in a variable. I then logically test that variable ( x=0 ) and branch accordingly. Yes, I know it is more steps and possible a extra microsecond of cpu time, but I can easily read it. Maybe when I am more familiar with scripting I can be more efficient.

Thanks for the help.

catkin · 02-16-2012, 10:27 AM

That's a valid way for a bash function to "return" data -- to write it into a global variable.

But if all you want is a succeed/fail then you may like to know about the bash idiom

Code:

if function_name arg1 arg2; then
    Do things you want if the function returned 0
else
    Do things you want if the function returned non-0
fi