--- install.c.orig	2003-11-01 13:46:59.000000000 +0200
+++ install.c	2003-11-01 15:09:14.000000000 +0200
@@ -92,6 +92,8 @@
 static void strip (const char *path);
 void usage (int status);
 
+static int issame (const char *from, const char *to);
+
 /* The name this program was run with, for error messages. */
 char *program_name;
 
@@ -119,9 +121,13 @@
 /* If nonzero, install a directory instead of a regular file. */
 static int dir_arg;
 
+/* If nonzero, compare source and destination files before overwriting */
+static int compare_files;
+
 static struct option const long_options[] =
 {
   {"backup", optional_argument, NULL, 'b'},
+  {"compare", no_argument, NULL, 'C'},
   {"directory", no_argument, NULL, 'd'},
   {"group", required_argument, NULL, 'g'},
   {"mode", required_argument, NULL, 'm'},
@@ -200,13 +206,14 @@
   group_name = NULL;
   strip_files = 0;
   dir_arg = 0;
+  compare_files = 0;
   umask (0);
 
   /* FIXME: consider not calling getenv for SIMPLE_BACKUP_SUFFIX unless
      we'll actually use backup_suffix_string.  */
   backup_suffix_string = getenv ("SIMPLE_BACKUP_SUFFIX");
 
-  while ((optc = getopt_long (argc, argv, "bcsDdg:m:o:pvV:S:", long_options,
+  while ((optc = getopt_long (argc, argv, "bcCsDdg:m:o:pvV:S:", long_options,
 			      NULL)) != -1)
     {
       switch (optc)
@@ -228,6 +235,9 @@
 	  break;
 	case 'c':
 	  break;
+	case 'C':
+	  compare_files = 1;
+	  break;
 	case 's':
 	  strip_files = 1;
 	  break;
@@ -436,6 +446,9 @@
       return 1;
     }
 
+  if (compare_files && issame(from,to))
+    return 0;
+
   fail = copy (from, to, nonexistent_dst, x, &copy_into_self, NULL);
 
   return fail;
@@ -510,6 +523,64 @@
   return 0;
 }
 
+/* Check if from and to are same
+   Return 0 if not, 1 if yes */
+
+#define CMP_BLKSIZE	4096
+#ifndef EINTR
+#  define EINTR 0
+#  define V_EINTR
+#endif
+static int
+issame (const char *from, const char *to)
+{
+  struct stat buf1, buf2;
+  char p1[CMP_BLKSIZE], p2[CMP_BLKSIZE];
+  ssize_t n_read1, n_read2;
+  int ret;
+  int fd1, fd2;
+
+  if (lstat(from, &buf1) || lstat(to, &buf2))
+    return 0;
+
+  if (buf1.st_size != buf2.st_size)
+    return 0;
+
+  if (!S_ISREG(buf1.st_mode) || !S_ISREG(buf2.st_mode))
+    return 0;
+
+  fd1=open(from, O_RDONLY); if (fd1<0) return 0;
+  fd2=open(to, O_RDONLY); if (fd2<0) { close (fd1); return 0; }
+
+  for (;;)
+  {
+    do {
+      n_read1=read(fd1, p1, CMP_BLKSIZE);
+      if (n_read1<0 && errno!=EINTR) { ret=0; goto do_return; }
+    } while (n_read1<0 && errno==EINTR);
+
+    do {
+      n_read2=read(fd2, p2, CMP_BLKSIZE);
+      if (n_read2<0 && errno!=EINTR) { ret=0; goto do_return; }
+    } while (n_read2<0 && errno==EINTR);
+
+   if (n_read1 == 0 && n_read2 == 0) { ret=1; goto do_return; }
+
+    if (n_read1!=n_read2) { ret=0; goto do_return; }
+
+    if (n_read1>0 && memcmp(p1, p2, n_read1)) { ret=0; goto do_return; }
+  }
+
+do_return:
+  close(fd1);
+  close(fd2);
+  return(ret);
+}
+#ifdef V_EINTR
+#  undef EINTR
+#endif
+#undef CMP_BLKSIZE
+
 /* Strip the symbol table from the file PATH.
    We could dig the magic number out of the file first to
    determine whether to strip it, but the header files and
@@ -613,6 +684,7 @@
       --backup[=CONTROL] make a backup of each existing destination file\n\
   -b                  like --backup but does not accept an argument\n\
   -c                  (ignored)\n\
+  -C, --compare       compare source and destination files before overwriting\n\
   -d, --directory     treat all arguments as directory names; create all\n\
                         components of the specified directories\n\
 "), stdout);