Your biggest problem is that your argument lists for your commands are malformed (after you've resolved the index 2 vs index 1 issue with the pipe file descriptors diagnosed by Ben Jackson in his answer).
I added a function:
static void dump_args(int pid, char **argv)
{
int i = 0;
fprintf(stderr, "args for %d:\n", pid);
while (*argv != 0)
fprintf(stderr, "%d: [%s]\n", i++, *argv++);
}
and called it just before the calls to execvp()
, and the output I got was:
$ ./ns
333sh: ls | sort
args for 29780:
0: [ls]
1: [|]
2: [sort]
ls: sort: No such file or directory
ls: |: No such file or directory
^C
$
The control-C was me interrupting the program. The arguments for each command must be 'the command name' (conventionally, the name of the executable), followed by the remaining arguments and a null pointer.
Your tokenization code is not providing two correct commands.
You also have a problem with which PID you're looking at:
cpid = fork();
if (cpid == 0)
{
dup2(fd[1], 1);
close(fd[0]);
close(fd[1]);
dump_args(getpid(), arg);
execvp(arg[0], arg);
fprintf(stderr, "Failed to exec %s\n", arg[0]);
exit(1);
}
else if (pid > 0) // should be cpid!
{
dup2(fd[0], 0);
close(fd[0]);
close(fd[1]);
dump_args(pid, arg);
execvp(arg[1], arg);
fprintf(stderr, "Failed to exec %s\n", arg[1]);
exit(1);
}
You also need to close the pipe file descriptors in the parent process before waiting.
This code compiles and 'works' for simple x | y
command sequences such as ls | sort
or ls | sort -r
. However, it is far from being a general solution; you'll need to fix your argument parsing code quite a lot before you reach a general solution.
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int setup(void);
int main(void)
{
while (1)
{
printf("333sh: ");
if (setup())
break;
}
return 0;
}
static void dump_args(int pid, char **argv)
{
int i = 0;
fprintf(stderr, "args for %d:\n", pid);
while (*argv != 0)
fprintf(stderr, "%d: [%s]\n", i++, *argv++);
}
int setup(void)
{
char input[128];
char *arg[32];
int i = 1;
while (fgets(input, sizeof(input), stdin) != NULL)
{
arg[0] = strtok(input, " \n");
while ((arg[i] = strtok(NULL, " \n")) != NULL)
{
i++;
}
if (arg[1] != NULL && strcmp(arg[1], "|") == 0 && arg[2] != NULL)
{
pid_t pid;
int fd[2];
arg[1] = NULL;
pipe(fd);
pid = fork();
if (pid < 0)
{
fprintf(stderr, "fork failed\n");
return 1;
}
else if (pid == 0)
{
pid_t cpid = fork();
if (cpid < 0)
{
fprintf(stderr, "fork failed\n");
return 1;
}
else if (cpid == 0)
{
printf("Writer: [%s]\n", arg[0]);
dup2(fd[1], 1);
close(fd[0]);
close(fd[1]);
dump_args(getpid(), arg);
execvp(arg[0], arg);
fprintf(stderr, "Failed to exec %s\n", arg[0]);
exit(1);
}
else
{
printf("Reader: [%s]\n", arg[2]);
assert(cpid > 0);
dup2(fd[0], 0);
close(fd[0]);
close(fd[1]);
dump_args(getpid(), &arg[2]);
execvp(arg[2], &arg[2]);
fprintf(stderr, "Failed to exec %s\n", arg[2]);
exit(1);
}
}
else
{
close(fd[0]);
close(fd[1]);
assert(pid > 0);
while (waitpid(pid, NULL, 0) != -1)
;
}
}
}
return 1;
}