2

Thanks for this Post it helped me a bit

returning value from called function in shell script

I have written a code like below :

File.c

i = system("/home/ubuntu/Documents/Flash_Desk_App/Project/test.sh -c");
printf("SH = %x",i);

test.sh

ONE=1   
echo " Hello world "        
clean()
    {        
    CLEAN_FLAG=1
    echo $ONE
    return "$ONE"    
    }

option="${1}"
case ${option} in
      -c) 
echo "Cleaning"
clean
;;  
    *) echo "Usage"
usage
;;
esac

but when i execute my ./a.out this is the output

Hello world 
Cleaning
1
SH = 0

IT ALWAYS PRINTS 0. CAN SOME ONE GUIDE ME IN SOLVING THIS. i WANT TO COLLECT THE VARIABLE VALUE RETURN BY SHELL IN MY C CODE.

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1
  • this is for some application.... ok i will remove the tag LDD.. any person from the lDD community can be aware of this..as we ahve lot to do with scripts Commented Apr 11, 2014 at 12:07

3 Answers 3

Reset to default
3

It is because the script is exiting with return code 0 (success). The exit status of a command is updated for every command that is executed. If you want to exit with the status of the clean command, you will need to do the following in your script:

EDIT - including full code to see the exact changes:

ONE=1   
echo " Hello world "  

# Initialize RC
rc=0

clean()
    {        
    CLEAN_FLAG=1
    echo $ONE
    return "$ONE"    
    }

option="${1}"
case ${option} in
      -c) 
echo "Cleaning"

# Run the clean command and capture the return code
clean
rc=$?

;;  
    *) echo "Usage"
usage
;;
esac

# Return the captured return code as our script's exit status.
exit $rc

Then it should work.

NOTE: you might get a different value in the C code (like 127) instead of 1. There is a strange mapping that takes place between shell exit codes and the return value of system calls from C.

An example executing this script from the bash shell:

$ ./test.sh -c
 Hello world 
Cleaning
1
$ echo $?
1

Thus, it can be executed as a system call from C and you can get the return code.

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17 Comments

thanks for your answer..but i need the return value from function..for which this might not be the soultion... i need the contents of $ONE in script
@user2598064 This should work for exactly that. Inside the script, you need to get the return code of the the clean function right after it is called. I've stored it in a variable rc. then, the rest of your script executes, and at the end, we exit test.sh with that return code. This makes the return code of the clean function available to external callers - like your C program!
@user2598064 A good way to try this kind of thing out is to execute a shell command and then echo $?. It will display the exit status (or return code) of the command. Run your original test.sh from the command prompt and see what the return code is (should be 0). Then make the changes I suggest and run it again. It should now have a return code of 1.
What type of shell are you using?
i think you have mentioned it wrongly as ?$ which should be $?
|
1

Besides the fact mentioned in Trenin's answer, apply the macro WEXITSTATUS to the value returned by system() to get the value returned by the command it executed.

From man 3 system:

RETURN VALUE

The value returned is -1 on error (e.g., fork(2) failed), and the return status of the command otherwise. This latter return status is in the format specified in wait(2). Thus, the exit code of the command will be WEXITSTATUS(status). In case /bin/sh could not be executed, the exit status will be that of a command that does exit(127).

The lesson learned here is: RTFM

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1 Comment

thanks for your answer..but i need the return value from function..for which this might not be the soultion
0

The above answers should all do. Better to make sure you get the right return value with your bash script first. 

# ./test.sh -c

# echo $?
1

(You can allways make changes to ONE=1) Then test it with your C code.. (don't forget to pass the return value from the (system) call to the WEXITSTATUS(i)) to get the right return value. 

{
    i = system("/home/ubuntu/Documents/Flash_Desk_App/Project/test.sh -c");
    i = WEXITSTATUS(i);
    printf("SH = %x",i);
}
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3 Comments

i think you people have not tried the complete loop for testing. i admire the return value from clean function is printed as one. but it is not printed as one in c program
if you try printing the value of $rc just above exit in test.h. you will find it is Zero.
SORRY FOR THE TROUBLE THIS WORKED WITH THE MACRO WEXITSTATUS. I was collecting the status in unsigned char which resulted in issue.... thanks alot for your interest

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