#!/bin/sh

echo "hello world!"

#include <stdlib.h>

main()
{
        system("./hello.sh");
}

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>

#define BUF_SIZE 256

int main(int argc, char *argv[]) {
	char * cmd;
	char buf[BUF_SIZE+1];
	int pipe_fd[2];
	int pid;
	FILE * in;
	int i;

	if (argc < 2) {
		printf("Usage: %s command\n", argv[0]);
		return 0;
	}

	cmd = argv[1];
	
	/* create a pipe */

	if (pipe(pipe_fd) != 0) {
		perror("pipe failed");
		return -1;
	}

	pid = fork();

	if (pid == 0) {
		/* child process */

		close(pipe_fd[0]);		/* no need to keep the read end
						   around */
		
		/* replace standard output */

		if (dup2(pipe_fd[1], 1) < 0) {
			perror("dup2 failed");
			close(pipe_fd[1]);
			return -1;
		}

		close(pipe_fd[1]);		/* no need for the original 
						   write end */

		if (execlp(cmd, cmd, NULL) == -1) {
			perror("execl failed");
		}

		close(1);
		return -1; 			/* only called if execl failed*/
	}

	/* server process */
	
	close(pipe_fd[1]); 			/* so the read end closes when 
					   	   the child process exits */

	in = fdopen(pipe_fd[0], "r");
	if (in == NULL) {
		fprintf(stderr, "Failed to open FILE from file descriptor\n");
		return -1;
	}


	while (fgets(buf, BUF_SIZE, in) != NULL) {
		for (i = 0; i < strlen(buf); i++) {
			buf[i] = toupper(buf[i]);
		}

		printf("%s", buf);
	}

	return 0;
}

#include <stdio.h>
#include <string.h>
#include <unistd.h>

#define MAXLINELEN 100
#define MAXCOMMAND 100
#define DISCARDSTDERR " 2>/dev/null"

int main(int argc, char *argv[])
{
    char line[MAXLINELEN + 1];
    char command[MAXCOMMAND + 1];
    FILE *pipe;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <name of man page>\n", argv[0]);
        return 1;
    }
    /* First construct a command line, (e.g. "man ls 2>/dev/null") with
     * safety checks for string length.
     */
    strncpy(command, "man", MAXCOMMAND);
    command[MAXCOMMAND] = '\0';
    if (strlen(command) + strlen(argv[1]) + strlen(DISCARDSTDERR) > MAXCOMMAND) {
        fprintf(stderr, "Error: Command would be too long (max = %d).\n", MAXCOMMAND);
        return 1;
    }
    strcat(command, " ");
    strcat(command, argv[1]);
    strcat(command, DISCARDSTDERR);  /* discard stderr: 2>/dev/null */

    /* Execute the command, setting up a pipe for getting its output. */
    pipe = popen(command, "r");
    if ((pipe = popen(command, "r")) == NULL) {
        perror("");
        return 1;
    }

    /* Read the doc from the pipe line-by-line, with a short delay */
    while (fgets(line, MAXLINELEN + 1, pipe) != NULL) {
        printf("%s", line);  /* fixed thx jlliagre */
        usleep(200000);
    }
    pclose(pipe);
    return 0;
}

printf(line);

printf("%s", line);