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I am writing a small linux shell in C and am so very close to being done. I take in a command from the user and store it in args, delimited by spaces. In the following example, let's say that args contains the following:
args[] = {"ls", "-l", "|", "wc"};
My function takes in args and also takes in how many pipes there are. I've commented my code as much as possible. Here it is:
int do_command(char **args, int pipes) {
// The number of commands to run
const int commands = pipes + 1;
int i = 0;
int pipefds[2*pipes];
for(i = 0; i < pipes; i++){
if(pipe(pipefds + i*2) < 0) {
perror("Couldn't Pipe");
exit(EXIT_FAILURE);
}
}
int pid;
int status;
int j = 0;
int k = 0;
int s = 1;
int place;
int commandStarts[10];
commandStarts[0] = 0;
// This loop sets all of the pipes to NULL
// And creates an array of where the next
// Command starts
while (args[k] != NULL){
if(!strcmp(args[k], "|")){
args[k] = NULL;
// printf("args[%d] is now NULL", k);
commandStarts[s] = k+1;
s++;
}
k++;
}
for (i = 0; i < commands; ++i) {
// place is where in args the program should
// start running when it gets to the execution
// command
place = commandStarts[i];
pid = fork();
if(pid == 0) {
//if not last command
if(i < pipes){
if(dup2(pipefds[j + 1], 1) < 0){
perror("dup2");
exit(EXIT_FAILURE);
}
}
//if not first command&& j!= 2*pipes
if(j != 0 ){
if(dup2(pipefds[j-2], 0) < 0){
perror("dup2");
exit(EXIT_FAILURE);
}