fork.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>

void split(char *buf, char** args, size_t sargs, size_t *nargs)
{
    char *bargs[sargs], **cp, *pbuf;
    int i, j;

    pbuf = bargs[0] = args[0] = buf;

    for(cp = bargs; (*cp = strsep(&pbuf, " \n\t")) != NULL;) if ((*cp != '\0') || (++cp >= &bargs[sargs])) break;

    for (i = j++; bargs[i] != NULL;) if(strlen(bargs[j]) > 0) args[i++]=bargs[j];

    *nargs = i;
    args[*nargs] = NULL;
}

int main(int argc, char *argv[])
{
    char buf[1<<16], *args[1<<16];

    int *status;
    size_t nargs;
    pid_t pid;

    while(1)
    {
        printf("$ ");
        fgets(buf, sizeof(buf), stdin);

        split(buf, args, sizeof(*args), &nargs);

        if (nargs == 0) continue;
        if (!strcmp(args[0], "exit")) exit(0);

        if (pid = fork()) pid = wait(status); else if( execvp(args[0], args)) exit(2);
    }
    return 0;
}