coreutils/readlink.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini readlink implementation for busybox
   4  *
   5  * Copyright (C) 2000,2001 Matt Kraai <kraai@alumni.carnegiemellon.edu>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8  */
   9 //config:config READLINK
  10 //config:       bool "readlink (4.8 kb)"
  11 //config:       default y
  12 //config:       help
  13 //config:       This program reads a symbolic link and returns the name
  14 //config:       of the file it points to
  15 //config:
  16 //config:config FEATURE_READLINK_FOLLOW
  17 //config:       bool "Enable canonicalization by following all symlinks (-f)"
  18 //config:       default y
  19 //config:       depends on READLINK
  20 //config:       help
  21 //config:       Enable the readlink option (-f).
  22
  23 //applet:IF_READLINK(APPLET_NOFORK(readlink, readlink, BB_DIR_USR_BIN, BB_SUID_DROP, readlink))
  24
  25 //kbuild:lib-$(CONFIG_READLINK) += readlink.o
  26
  27 //usage:#define readlink_trivial_usage
  28 //usage:        IF_FEATURE_READLINK_FOLLOW("[-fnv] ")
  29 //usage:        IF_NOT_FEATURE_READLINK_FOLLOW("[-n] ")
  30 //usage:        "FILE"
  31 //usage:#define readlink_full_usage "\n\n"
  32 //usage:       "Display the value of a symlink" "\n"
  33 //usage:     "\n        -n      Don't add newline"
  34 //usage:        IF_FEATURE_READLINK_FOLLOW(
  35 //usage:     "\n        -f      Canonicalize by following all symlinks"
  36 //usage:     "\n        -v      Verbose"
  37 //usage:        )
  38
  39 #include "libbb.h"
  40
  41 /*
  42  * # readlink --version
  43  * readlink (GNU coreutils) 6.10
  44  * # readlink --help
  45  *   -f, --canonicalize
  46  *      canonicalize by following every symlink in
  47  *      every component of the given name recursively;
  48  *      all but the last component must exist
  49  *   -e, --canonicalize-existing
  50  *      canonicalize by following every symlink in
  51  *      every component of the given name recursively,
  52  *      all components must exist
  53  *   -m, --canonicalize-missing
  54  *      canonicalize by following every symlink in
  55  *      every component of the given name recursively,
  56  *      without requirements on components existence
  57  *   -n, --no-newline              do not output the trailing newline
  58  *   -q, --quiet, -s, --silent     suppress most error messages
  59  *   -v, --verbose                 report error messages
  60  *
  61  * bbox supports: -f (partially) -n -v (fully), -q -s (accepts but ignores)
  62  * Note: we export the -f flag, but our -f behaves like coreutils' -e.
  63  * Unfortunately, there isn't a C lib function we can leverage to get this
  64  * behavior which means we'd have to implement the full stack ourselves :(.
  65  */
  66
  67 int readlink_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  68 int readlink_main(int argc UNUSED_PARAM, char **argv)
  69 {
  70         char *buf;
  71         unsigned opt;
  72
  73         /* -n must use bit 0 (see printf below) */
  74         opt = getopt32(argv, "^" "n" IF_FEATURE_READLINK_FOLLOW("fvsq")
  75                        "\0" "=1");
  76
  77         /* compat: coreutils readlink reports errors silently via exit code */
  78         if (!(opt & 4)) /* not -v */
  79                 logmode = LOGMODE_NONE;
  80
  81         /* NOFORK: only one alloc is allowed; must free */
  82         if (opt & 2) { /* -f */
  83                 buf = xmalloc_realpath_coreutils(argv[optind]);
  84         } else {
  85                 buf = xmalloc_readlink_or_warn(argv[optind]);
  86         }
  87
  88         if (!buf)
  89                 return EXIT_FAILURE;
  90         printf("%s%s", buf, &"\n"[opt & 1]);
  91         free(buf);
  92
  93         fflush_stdout_and_exit_SUCCESS();
  94 }