Child process cannot get the input from stdin written by parent process - linux

Question

In child process, I use execl() to execute a program "test1" with the input from stdin. However, the input from stdin cannot be passed to "test1", but it is fine for "sort" command.
example.c
#include <unistd.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
int fds[2]; // an array that will hold two file descriptors
pipe(fds); // populates fds with two file descriptors
pid_t pid = fork(); // create child process that is a clone of the parent
if (pid == 0) { // if pid == 0, then this is the child process
dup2(fds[0], STDIN_FILENO); // fds[0] (the read end of pipe) donates its data to file descriptor 0
close(fds[0]); // file descriptor no longer needed in child since stdin is a copy
close(fds[1]); // file descriptor unused in child
//if (execl("/usr/bin/sort", "sort", (char *)0) < 0) exit(0);//working
if (execl("./test1", "test1", (char *)0) < 0) exit(0);//not working
}
// if we reach here, we are in parent process
close(fds[0]); // file descriptor unused in parent
const char *words[] = {"pear", "peach", "apple"};
// write input to the writable file descriptor so it can be read in from child:
size_t numwords = sizeof(words)/sizeof(words[0]);
for (size_t i = 0; i < numwords; i++) {
dprintf(fds[1], "%s\n", words[i]);
}
// send EOF so child can continue (child blocks until all input has been processed):
close(fds[1]);
int status;
pid_t wpid = waitpid(pid, &status, 0); // wait for child to finish before exiting
return wpid == pid && WIFEXITED(status) ? WEXITSTATUS(status) : -1;
}
For "sort" command, the output is:
$ ./example
apple
peach
pear
For "test1" , the output is:
$ ./example
hello!
test1
If it is working for "test1", the output should be:
$ ./test1 pear peach apple
hello!
./test1
pear
peach
apple
test1.c
#include<stdio.h>
#include<stdlib.h>
int main(int argc, char** argv){
printf("hello!\n");
for(int i = 0; i < argc; i++){
printf("%s\n", argv[i]);
}
return 0;
}
What am I doing wrong?

Answer 1

test1 doesn't read any input, so passing it input doesn't work.
To get your sample output have test1 execl cat.