whotofile.c

介绍和编写和IO重定向的使用

/* whotofile.c
 *	purpose: show how to redirect output for another program
 *	   idea: fork, then in the child, redirect output, then exec
 */
#include	<stdio.h>

main()
{
	int	pid ;
	int	fd;

	printf("About to run who into a file\n");

	/* create a new process or quit */
	if( (pid = fork() ) == -1 ){
		perror("fork"); exit(1);
	}
	/* child does the work */
	if ( pid == 0 ){
		close(1);				/* close, */
		fd = creat( "userlist", 0644 );		/* then open */
		execlp( "who", "who", NULL );		/* and run	*/
		perror("execlp");
		exit(1);
	}
	/* parent waits then reports */
	if ( pid != 0 ){
		wait(NULL);
		printf("Done running who.  results in userlist\n");
	}
}