example/posix/processes-launcher.c

Shows how to execute commands in subprocesses

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>

// parses a command line, forks, executes
// the command in the child process and waits
// for it to finish
bool parse_exec_and_wait(char* cmd_line)
{
    // fork
    pid_t pid = fork();
    // if there was an error complain and quit
    if(pid < 0)
    {
        perror("Fork failed");
        return false;
    }
    // if we are in the child process
    else if(pid == 0)
    {
        size_t max_args = 31;
        char* args[32];
        int arg = 0;

        // parse the command line strings
        char *p, *s;
        const char *delim = " \t\r\n\0";
        p = strtok_r(cmd_line, delim, &s);
        while(p)
        {
            if(arg == max_args) break;
            args[arg++] = p;
            p = strtok_r(NULL, delim, &s);
        }
        // terminate the list of arguments
        args[arg] = NULL;
        // execute the command
        execvp(args[0], args);
        // if we're here something went wrong
        // complain and exit
        printf("Failed to execute '%s'\n", cmd_line);
        return false;
    }
    // if we are in the parent process
    else
    {
        // wait for the child to finish
        int status = 0;
        waitpid(pid, &status, 0);
        if(WIFSIGNALED(status))
            printf("Terminated by signal %d\n", WTERMSIG(status));
    }
    return true;
}

int main(int argc, const char* argv[])
{
    // a buffer for the command line
    size_t size = 1023;
    char buffer[1024];
    // print the prompt and read a single line
    while(fputs("$>", stdout), fgets(buffer, size, stdin))
    {
        // terminate the string (just in case)
        buffer[size] = '\0';

        // if the user typed 'exit' - exit
        if(strncmp(buffer, "exit", 4) == 0) break;
        // otherwise parse and execute the command
        else if(!parse_exec_and_wait(buffer)) return 1;
    }
    fputc('\n', stdout);
    return 0;
}