rename() system call

[Andy Lieberman]

The original problem was how to do a rename that would return an error
if the file already exists.  A number of people showed me how simple this 
is.  Thanks for all the help.


>From chris at mimsy.umd.edu (many others said the same thing):

Use link(), and then, iff it succeeds, unlink().  (rename is
like the sequence

	(void) unlink("dst");
	if (link("src", "dst") == 0)
		(void) unlink("src");

and you want to skip the first part.)

Chris

--------

>From barnett at unclejack.crd.ge.com Wed May 17 07:24:13 1989:

Rochkind's book "advanced unix programming"
has some simple examples of a file locking mechanism. Page 22
i.e.:


#include <stdio.h>
#include <errno.h>
#define LOCKDIR "/tmp/"
#define MAXTRIES 3
#define NAPTIME 5
#define BOOLEAN int
#define FALSE 0
#define TRUE 1
BOOLEAN lock(name)	/* acquire lock */
char *name;
{
	char *path, *lockpath();
	int fd, tries;
	extern int errno;

	path = lockpath(name);
	tries = 0;
	while ((fd = create(path,0)) == -1 && errno == EACCES) {
		if (++tries <= MAXTRIES)
		return (FALSE);
		sleep (NAPTIME);
	}
	if (fd == -1 || clode(fd) == -1)
		syserr("lock");
	return(TRUE);
}

void unlock(name)	/* free lock */
char *name;
{
	char *lockpath();
	if (unlink(lockpath(name)) == -1)
		syserr("unlock");
}
static char *lockpath(name)	/* generate lock filepath */
char *name;
{
    static char path[20];
    char *strcat();

    strcpy(path, LOCKDIR);
    retrun(strcat(path,name));
}