6.10. 競合状態を避ける

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>

void failure(msg) {
 fprintf(stderr, "%s\n", msg);
 exit(1);
}

/*
 * Given a "pattern" for a temporary filename
 * (starting with the directory location and ending in XXXXXX),
 * create the file and return it.
 * This routines unlinks the file, so normally it won't appear in
 * a directory listing.
 * The pattern will be changed to show the final filename.
 */

FILE *create_tempfile(char *temp_filename_pattern)
{
 int temp_fd;
 mode_t old_mode;
 FILE *temp_file;

 old_mode = umask(077);  /* Create file with restrictive permissions */
 temp_fd = mkstemp(temp_filename_pattern);
 (void) umask(old_mode);
 if (temp_fd == -1) {
   failure("Couldn't open temporary file");
 }
 if (!(temp_file = fdopen(temp_fd, "w+b"))) {
   failure("Couldn't create temporary file's file descriptor");
 }
 if (unlink(temp_filename_pattern) == -1) {
   failure("Couldn't unlink temporary file");
 }
 return temp_file;
}


/*
 * Given a "tag" (a relative filename ending in XXXXXX),
 * create a temporary file using the tag.  The file will be created
 * in the directory specified in the environment variables
 * TMPDIR or TMP, if defined and we aren't setuid/setgid, otherwise
 * it will be created in /tmp.  Note that root (and su'd to root)
 * _will_ use TMPDIR or TMP, if defined.
 * 
 */
FILE *smart_create_tempfile(char *tag)
{
 char *tmpdir = NULL;
 char *pattern;
 FILE *result;

 if ((getuid()==geteuid()) && (getgid()==getegid())) {
   if (! ((tmpdir=getenv("TMPDIR")))) {
     tmpdir=getenv("TMP");
   }
 }
 if (!tmpdir) {tmpdir = "/tmp";}

 pattern = malloc(strlen(tmpdir)+strlen(tag)+2);
 if (!pattern) {
   failure("Could not malloc tempfile pattern");
 }
 strcpy(pattern, tmpdir);
 strcat(pattern, "/");
 strcat(pattern, tag);
 result = create_tempfile(pattern);
 free(pattern);
 return result;
}



main() {
 int c;
 FILE *demo_temp_file1;
 FILE *demo_temp_file2;
 char demo_temp_filename1[] = "/tmp/demoXXXXXX";
 char demo_temp_filename2[] = "second-demoXXXXXX";

 demo_temp_file1 = create_tempfile(demo_temp_filename1);
 demo_temp_file2 = smart_create_tempfile(demo_temp_filename2);
 fprintf(demo_temp_file2, "This is a test.\n");
 printf("Printing temporary file contents:\n");
 rewind(demo_temp_file2);
 while (  (c=fgetc(demo_temp_file2)) != EOF) {
   putchar(c);
 }
 putchar('\n');
 printf("Exiting; you'll notice that there are no temporary files on exit.\n");
}

 char *filename;
 int fd;

 do {
   filename = tempnam (NULL, "foo");
   fd = open (filename, O_CREAT | O_EXCL | O_TRUNC | O_RDWR, 0600);
   free (filename);
 } while (fd == -1);

   echo "This is a test" > /tmp/test$$  # DON'T DO THIS.

 # Simple use of mktemp(1), where the script should quit
 # if it can't get a safe temporary file:

   TMPFILE=`mktemp /tmp/$0.XXXXXX` || exit 1
   echo "program output" >> $TMPFILE

  # Simple example, if you want to catch the error:

   TMPFILE=`mktemp -q /tmp/$0.XXXXXX`
   if [ $? -ne 0 ]; then
      echo "$0: Can't create temp file, exiting..."
      exit 1
   fi