CODEWITHSUNDEEP
cshellembedded-linux
user2598064
user2598064

Reputation: 157

Collecting return value from Shell Script

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.

Upvotes: 2

Views: 7787

Answers (3)

Ari
Ari

Reputation: 92

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);
}

Upvotes: 0

Trenin
Trenin

Reputation: 2063

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.

Upvotes: 3

alk
alk

Reputation: 70901

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

Upvotes: 1

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