This C program executes multiple commands piped together by using fork() and pipe() system calls. It parses each command and its parameters into a linked list. The execommands() function iterates through the list, forking a child process for each intermediate command. The child process duplicates the pipe file descriptor to stdin or stdout as needed, closes the unneeded file descriptor, and executes the command using execvp(). After the child process exits, the parent process waits and continues to the next command.

1. // C Program
How might I modify this code to handle any number of commands piped together? such as ls |
wc or ls | wc -l | ps -elf etc..
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
// keeps track of cmd parameters
typedef struct param {
char *param;
struct param *next;
} pt;
// parses individual commands
typedef struct cmd_list {
char *cmd;
int param_count;
pt *param_list;
char * input_file_name;
char *output_file_name;
struct cmd_list *next;
} cl;
// keeps track of main commands that are piped

2. typedef struct list {
cl *head;
cl *tail;
int count;
} pt;
void execommands(clt *cmds) {
clt *cmd = cmds;
for (int i = 1; i < cmds->count-1; i++) {
int pipes[2] = {-1, -1};
pid_t pid = -1;
clt *temp = NULL;
pipe(pipes);
pid = fork();
switch (pid) {
case -1:
perror("fork failed");
break;
case 0:
{
char **rhp_argv = NULL;
char *rhp = NULL;
pt *temp = NULL;
int i = 1;

3. int flag_count = 0;
char flag_string[100] = "";
temp = cmd->param_list;
if (dup2(pipes[STDIN_FILENO], STDIN_FILENO) < 0) {
perror("child process failed dup2");
_exit(EXIT_FAILURE);
}
close(pipes[STDIN_FILENO]);
close(pipes[STDOUT_FILENO]);
rhp = cmd->cmd;
if(0 != cmd->param_count) {
rhp_argv = (char **) calloc((cmd->param_count), sizeof(char *));
rhp_argv[0] = rhp;
while(temp != NULL) {
if (flag_count > 0 && temp->param[0] == '-')
memmove(temp->param, temp->param + 1, strlen(temp->param));
}
strcat(flag_string, temp->param)
flag_count++;
temp = temp->next
}
rhp_argv[i] = strdup(flag_string);

4. i++;
}
else {
rhp_argv = (char **) calloc(2, sizeof(char *));
rhp_argv[0] = rhp;
}
execvp(rhp_argv[0], rhp_argv);
perror("child cannot exec program");
_exit(EXIT_FAILURE);
if(cmd->param_count != 0) {
for(int celm = 0; celm < flag_count; i++) {
free(rhp_argv[i]);
rhp_argv[i] = NULL;
}
}
free(rhp_argv);
rhp_argv = NULL;
free(temp);
}
break;
default:
int status;
waitpid(pid, &status, 0);

5. break;
} // end switch
} // end for
}