Thread: Child process status when command doesn't exist/path iis worng

  1. #1
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    Child process status when command doesn't exist/path iis worng

    Hi, I have this program which gets two arguments as parameters and runs it in linux:

    Code:
    
     int main(int argc, char *argv[])
    {
     
        int status;
        pid_t pid;
        pid = fork();
        if(pid == 0)
           execvp(argv[1],argv+1);
        else if (pid >0) {
                /*this is the part of the code I'm missing*/
                }
        return 0;
    }
    I need to capture if the parameters passed are not a valid UX command.
    I've tried WIFEXITED and WEXISTSTATUS but they always return "1" whether it's a valid linux command or not. Is there a way to know if the linux command wwhich the child process is running doesn't exist?
    Last edited by Sergi; 05-12-2019 at 05:49 AM.

  2. #2
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    Quote Originally Posted by Sergi View Post
    I need to capture if the parameters passed are not a valid UX command.
    I've tried WIFEXITED and WEXISTSTATUS but they always return "1" whether it's a valid linux command or not. Is there a way to know if the linux command wwhich the child process is running doesn't exist?
    fork() returns the PID of the child process in the forked process, 0 in the child process or -1 in case of error.

  3. #3
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    Quote Originally Posted by flp1969 View Post
    fork() returns the PID of the child process in the forked process, 0 in the child process or -1 in case of error.

    My question is, what status is returned when the UX command the child is executing doesn't exist or can't be executed because it's a wrong path?

    I'm asking because I'm using WIFEXITED(status) and WEXITSTATUS(status) and they return 1, even when the commands I feed to the program are not linux commands.

  4. #4
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    Quote Originally Posted by Sergi View Post
    I'm asking because I'm using WIFEXITED(status) and WEXITSTATUS(status) and they return 1, even when the commands I feed to the program are not linux commands.
    These macros are applied only to the status returned as the first argument of wait() function. wait() returns (in its argument) the status (exit code) of child processes only.

    WIFEXITED() returns a boolean: 1 if the child process has exited, 0 otherwise.
    WEXITSTATUS() returns the exit code of the process.

    fork() will return -1 if it cannot fork the current process (and set errno with the error)... exec() functions will return ONLY if an error occurs (and errno will NOT be changed)... So, if execvp() returns, you can assume the command is wrong (doesn't exist or cannot be spawned)...

    See 'man 3 wait' and "man execvp" for more details.

  5. #5
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    Will look into that, thanks for your help.

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