coreutils/ln.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini ln implementation for busybox
   4  *
   5  * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8  */
   9 //config:config LN
  10 //config:       bool "ln (5.1 kb)"
  11 //config:       default y
  12 //config:       help
  13 //config:       ln is used to create hard or soft links between files.
  14
  15 //applet:IF_LN(APPLET_NOEXEC(ln, ln, BB_DIR_BIN, BB_SUID_DROP, ln))
  16
  17 //kbuild:lib-$(CONFIG_LN) += ln.o
  18
  19 /* BB_AUDIT SUSv3 compliant */
  20 /* BB_AUDIT GNU options missing: -d, -F, -i, and -v. */
  21 /* http://www.opengroup.org/onlinepubs/007904975/utilities/ln.html */
  22
  23 //usage:#define ln_trivial_usage
  24 //usage:       "[-sfnbtv] [-S SUF] TARGET... LINK|DIR"
  25 //usage:#define ln_full_usage "\n\n"
  26 //usage:       "Create a link LINK or DIR/TARGET to the specified TARGET(s)\n"
  27 //usage:     "\n        -s      Make symlinks instead of hardlinks"
  28 //usage:     "\n        -f      Remove existing destinations"
  29 //usage:     "\n        -n      Don't dereference symlinks - treat like normal file"
  30 //usage:     "\n        -b      Make a backup of the target (if exists) before link operation"
  31 //usage:     "\n        -S SUF  Use suffix instead of ~ when making backup files"
  32 //usage:     "\n        -T      Treat LINK as a file, not DIR"
  33 //usage:     "\n        -v      Verbose"
  34 //usage:
  35 //usage:#define ln_example_usage
  36 //usage:       "$ ln -s BusyBox /tmp/ls\n"
  37 //usage:       "$ ls -l /tmp/ls\n"
  38 //usage:       "lrwxrwxrwx    1 root     root            7 Apr 12 18:39 ls -> BusyBox*\n"
  39
  40 #include "libbb.h"
  41
  42 /* This is a NOEXEC applet. Be very careful! */
  43
  44 #define LN_SYMLINK          (1 << 0)
  45 #define LN_FORCE            (1 << 1)
  46 #define LN_NODEREFERENCE    (1 << 2)
  47 #define LN_BACKUP           (1 << 3)
  48 #define LN_SUFFIX           (1 << 4)
  49 #define LN_VERBOSE          (1 << 5)
  50 #define LN_LINKFILE         (1 << 6)
  51
  52 int ln_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  53 int ln_main(int argc, char **argv)
  54 {
  55         exitcode_t status = EXIT_SUCCESS;
  56         int opts;
  57         char *last;
  58         char *src_name;
  59         char *src;
  60         char *suffix = (char*)"~";
  61         struct stat statbuf;
  62         int (*link_func)(const char *, const char *);
  63
  64         opts = getopt32(argv, "^" "sfnbS:vT" "\0" "-1", &suffix);
  65 /*
  66         -s, --symbolic          make symbolic links instead of hard links
  67         -f, --force             remove existing destination files
  68         -n, --no-dereference    treat LINK_NAME as a normal file if it is a symbolic link to a directory
  69         -b                      like --backup but does not accept an argument
  70         --backup[=CONTROL]      make a backup of each existing destination file
  71         -S, --suffix=SUFFIX     override the usual backup suffix
  72         -v, --verbose
  73         -T, --no-target-directory
  74         -d, -F, --directory     allow the superuser to attempt to hard link directories
  75         -i, --interactive       prompt whether to remove destinations
  76         -L, --logical           dereference TARGETs that are symbolic links
  77         -P, --physical          make hard links directly to symbolic links
  78         -r, --relative          create symbolic links relative to link location
  79         -t, --target-directory=DIRECTORY        specify the DIRECTORY in which to create the links
  80  */
  81         last = argv[argc - 1];
  82         argv += optind;
  83         argc -= optind;
  84
  85         if ((opts & LN_LINKFILE) && argc > 2) {
  86                 bb_simple_error_msg_and_die("-T accepts 2 args max");
  87         }
  88
  89         if (!argv[1]) {
  90                 /* "ln PATH/TO/FILE" -> "ln PATH/TO/FILE FILE" */
  91                 *--argv = last;
  92                 /* xstrdup is needed: "ln -s PATH/TO/FILE/" is equivalent to
  93                  * "ln -s PATH/TO/FILE/ FILE", not "ln -s PATH/TO/FILE FILE"
  94                  */
  95                 last = bb_get_last_path_component_strip(xstrdup(last));
  96         }
  97
  98         do {
  99                 src_name = NULL;
 100                 src = last;
 101
 102                 if (is_directory(src,
 103                                 /*followlinks:*/ !(opts & (LN_NODEREFERENCE|LN_LINKFILE))
 104                                 /* Why LN_LINKFILE does not follow links:
 105                                  * -T/--no-target-directory implies -n/--no-dereference
 106                                  */
 107                                 )
 108                 ) {
 109                         if (opts & LN_LINKFILE) {
 110                                 bb_error_msg_and_die("'%s' is a directory", src);
 111                         }
 112                         src_name = xstrdup(*argv);
 113                         src = concat_path_file(src, bb_get_last_path_component_strip(src_name));
 114                         free(src_name);
 115                         src_name = src;
 116                 }
 117                 if (!(opts & LN_SYMLINK) && stat(*argv, &statbuf)) {
 118                         // coreutils: "ln dangling_symlink new_hardlink" works
 119                         if (lstat(*argv, &statbuf) || !S_ISLNK(statbuf.st_mode)) {
 120                                 bb_simple_perror_msg(*argv);
 121                                 status = EXIT_FAILURE;
 122                                 free(src_name);
 123                                 continue;
 124                         }
 125                 }
 126
 127                 if (opts & LN_BACKUP) {
 128                         char *backup;
 129                         backup = xasprintf("%s%s", src, suffix);
 130                         if (rename(src, backup) < 0 && errno != ENOENT) {
 131                                 bb_simple_perror_msg(src);
 132                                 status = EXIT_FAILURE;
 133                                 free(backup);
 134                                 continue;
 135                         }
 136                         free(backup);
 137                         /*
 138                          * When the source and dest are both hard links to the same
 139                          * inode, a rename may succeed even though nothing happened.
 140                          * Therefore, always unlink().
 141                          */
 142                         unlink(src);
 143                 } else if (opts & LN_FORCE) {
 144                         unlink(src);
 145                 }
 146
 147                 link_func = link;
 148                 if (opts & LN_SYMLINK) {
 149                         link_func = symlink;
 150                 }
 151
 152                 if (opts & LN_VERBOSE) {
 153                         printf("'%s' -> '%s'\n", src, *argv);
 154                 }
 155
 156                 if (link_func(*argv, src) != 0) {
 157                         bb_simple_perror_msg(src);
 158                         status = EXIT_FAILURE;
 159                 }
 160
 161                 free(src_name);
 162         } while ((++argv)[1]);
 163
 164         return status;
 165 }