stdinredir1.c

unix linux 编程实践源代码

/* stdinredir1.c
 *	purpose: show how to redirect standard input by replacing file 
 *		 descriptor 0 with a connection to a file.
 *	 action: reads three lines from standard input, then
 *		 closes fd 0, opens a disk file, then reads in
 *		 three more lines from standard input
 */
#include	<stdio.h>
#include	<fcntl.h>

main()
{
	int	fd ;
	char	line[100];

	/* read and print three lines */

	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );

	/* redirect input */

	close(0);
	fd = open("/etc/passwd", O_RDONLY);
	if ( fd != 0 ){
		fprintf(stderr,"Could not open data as fd 0\n");
		exit(1);
	}

	/* read and print three lines */

	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );
}