Forking with Pipes
- by Luke
Hello
I have tried to do fork() and piping in main and it works perfectly fine but when I try to implement it in a function for some reason I don't get any output, this is my code:
void cmd(int **pipefd,int count,int type, int last);
int main(int argc, char *argv[]) {
int pipefd[3][2];
int i, total_cmds = 3,count = 0;
int in = 1;
for(i = 0; i < total_cmds;i++){
pipe(pipefd[count++]);
cmd(pipefd,count,i,0);
}
/*Last Command*/
cmd(pipefd,count,i,1);
exit(EXIT_SUCCESS);
}
void cmd(int **pipefd,int count,int type, int last){
int child_pid,i,i2;
if ((child_pid = fork()) == 0) {
if(count == 1){
dup2(pipefd[count-1][1],1); /*first command*/
}
else if(last!=0){
dup2(pipefd[count - 2][0],0); /*middle commands*/
dup2(pipefd[count - 1][1],1);
}
else if(last == 1){
dup2(pipefd[count - 1][0],0); /*last command*/
}
for(i = 0; i < count;i++){/*close pipes*/
for(i2 = 0; i2 < 2;i2++){
close(pipefd[i][i2]);
}}
if(type == 0){
execlp("ls","ls","-al",NULL);
}
else if(type == 1){
execlp("grep","grep",".bak",NULL);
}
else if(type==2){
execl("/usr/bin/wc","wc",NULL);
}
else if(type ==3){
execl("/usr/bin/wc","wc","-l",NULL);
}
perror("exec");
exit(EXIT_FAILURE);
}
else if (child_pid < 0) {
perror("fork");
exit(EXIT_FAILURE);
}
}
I checked the file descriptors and it is opening the right ones, not sure what the problem
could be..
