/* 
 * redir.c: sample program showing how to redirect stdout and process
 * the argument vector.
 *
 * Stefan Brandle, COS 421, February 2000.
 */

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

int main( int argc, char *argv[], char *envp[] )
{
    int redir_fd;	/* File descriptor holder for argv[1] */

    if( argc != 2 ) {
	fprintf( stderr, "%s: usage is '%s OutputFileForStdout'\n",
                 	 argv[0], argv[0] );
        return 1;
    }

    /*  
     *  Now get to work. Duplicate stdout to argv[1]. Steps:
     *  1) First open argv[1] & make sure that opened.
     *  2) Then dup2() argv[1] file descriptor onto stdout file descriptor.
     *     We now have 2 file descriptors pointing to the same place (argv[1]).
     *  3) Then close argv[1] file descriptor. Stdout is left pointing to
     *     argv[1].
     */

    redir_fd = open( argv[1], O_CREAT|O_WRONLY|O_TRUNC );
    if( redir_fd == -1 ) {
	fprintf( stderr, "%s: error openning file %s.\n", argv[0], argv[1] );
        return 2;
    }

    if( dup2( redir_fd, 1 ) == -1 ) {
	fprintf( stderr, "%s: error performing dup2 on %s.\n",
                         argv[0], argv[1] );
        return 3;
    }

    close( redir_fd );

    /* Now to write to stdout and have it show up in argv[1] */
    printf( "Look, mom, redirected file I/O!\n." );

    return 0;
}