C script for piping input onto n pipes for further processing

pipn.c

#!/bin/bash
exc=/tmp/pipn.c
if [ $0 -nt $exc ]; then sed -n "/^\/\*\*$/,\$p" $0 | gcc -x c - -o $exc; fi

cat | $exc "$@"

exit
/**
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#define siz 1024

char cmds[siz];
char *cmd(char *s)
{
  assert(10 < sprintf(cmds, "bash -c \"%s\"", s));
  return cmds;
}

int main(int argc, char *argv[])
{
  char buf[siz];
  FILE **pip;
  assert(argc>1);
  int i, r, n = argc-1;
  assert(pip = malloc(n*sizeof(FILE *)));

  for(i=0; i<n; ++i)     assert(pip[i] = popen(cmd(argv[i+1]), "w"));

  r = fread(buf, 1, siz, stdin);
  while (r > 0)
  {
    for(i=0; i<n; ++i)  assert(r == fwrite(buf, 1, r, pip[i]));

    r = fread(buf, 1, siz, stdin);
  }

  for(i=0; i<n; ++i)    assert(-1 != pclose(pip[i]));
  free(pip);

  return 0;
}

https://www.raspberrypi.org/forums/viewtopic.php?f=33&t=319473&p=1913242#p1913242
Demo with 3 pipes:

$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | ./pipn.c "head -3" "wc" "tail -2"
1
2
3
     10      10      21
9
10
$ 

Now demo with "pipe in pipe":

$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | ./pipn.c "head -3 | wc" "tail -2"
      3       3       6
9
10
$