bsd/man/man2/readlink.2

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  34 .\"     @(#)readlink.2  8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt READLINK 2
  38 .Os BSD 4.2
  39 .Sh NAME
  40 .Nm readlink ,
  41 .Nm readlinkat
  42 .Nd read value of a symbolic link
  43 .Sh SYNOPSIS
  44 .Fd #include <unistd.h>
  45 .Ft  ssize_t
  46 .Fo readlink
  47 .Fa "const char *restrict path"
  48 .Fa "char *restrict buf"
  49 .Fa "size_t bufsize"
  50 .Fc
  51 .Ft ssize_t
  52 .Fo readlinkat
  53 .Fa "int fd" "const char *restrict path" "char *restrict buf" "size_t bufsize"
  54 .Fc
  55 .Sh DESCRIPTION
  56 .Fn readlink
  57 places the contents of the symbolic link
  58 .Fa path
  59 in the buffer
  60 .Fa buf ,
  61 which has size
  62 .Fa bufsize .
  63 .Nm Readlink
  64 does not append a
  65 .Dv NUL
  66 character to
  67 .Fa buf .
  68 .Pp
  69 The
  70 .Fn readlinkat
  71 system call is equivalent to
  72 .Fn readlink
  73 except in the case where
  74 .Fa path
  75 specifies a relative path.
  76 In this case the symbolic link whose content is read relative to the
  77 directory associated with the file descriptor
  78 .Fa fd
  79 instead of the current working directory.
  80 If
  81 .Fn readlinkat
  82 is passed the special value
  83 .Dv AT_FDCWD
  84 in the
  85 .Fa fd
  86 parameter, the current working directory is used and the behavior is
  87 identical to a call to
  88 .Fn readlink .
  89 .Sh RETURN VALUES
  90 The call returns the count of characters placed in the buffer
  91 if it succeeds, or a -1 if an error occurs, placing the error
  92 code in the global variable
  93 .Va errno .
  94 .Sh ERRORS
  95 .Fn readlink
  96 will fail if:
  97 .Bl -tag -width Er
  98 .\" ===========
  99 .It Bq Er EACCES
 100 Search permission is denied for a component of the path prefix.
 101 .\" ===========
 102 .It Bq Er EFAULT
 103 .Fa Buf
 104 extends outside the process's allocated address space.
 105 .\" ===========
 106 .It Bq Er EINVAL
 107 The named file is not a symbolic link.
 108 .\" ===========
 109 .It Bq Er EIO
 110 An I/O error occurred while reading from the file system.
 111 .\" ===========
 112 .It Bq Er ELOOP
 113 Too many symbolic links are encountered in translating the pathname.
 114 This is taken to be indicative of a looping symbolic link.
 115 .\" ===========
 116 .It Bq Er ENAMETOOLONG
 117 A component of a pathname exceeded
 118 .Dv {NAME_MAX}
 119 characters, or an entire path name
 120 (possibly expanded by a symbolic link) exceeded
 121 .Dv {PATH_MAX}
 122 characters.
 123 .\" ===========
 124 .It Bq Er ENOENT
 125 The named file does not exist.
 126 .\" ===========
 127 .It Bq Er ENOTDIR
 128 A component of the path prefix is not a directory.
 129 .El
 130 .Pp
 131 In addition to the errors returned by the
 132 .Fn readlink ,
 133 the
 134 .Fn readlinkat
 135 may fail if:
 136 .Bl -tag -width Er
 137 .It Bq Er EBADF
 138 The
 139 .Fa path
 140 argument does not specify an absolute path and the
 141 .Fa fd
 142 argument is neither
 143 .Dv AT_FDCWD
 144 nor a valid file descriptor open for searching.
 145 .It Bq Er ENOTDIR
 146 The
 147 .Fa path
 148 argument is not an absolute path and
 149 .Fa fd
 150 is neither
 151 .Dv AT_FDCWD
 152 nor a file descriptor associated with a directory.
 153 .El
 154 .Sh LEGACY SYNOPSIS
 155 .Fd #include <unistd.h>
 156 .Pp
 157 .Ft int
 158 .br
 159 .Fo readlink
 160 .Fa "const char *path"
 161 .Fa "char *buf"
 162 .Fa "int bufsize"
 163 .Fc ;
 164 .Pp
 165 The function type and the type of
 166 .Fa bufsize
 167 have changed.
 168 .Sh SEE ALSO
 169 .Xr lstat 2 ,
 170 .Xr stat 2 ,
 171 .Xr symlink 2 ,
 172 .Xr compat 5 ,
 173 .Xr symlink 7
 174 .Sh STANDARDS
 175 The
 176 .Fn readlinkat
 177 system call is expected to conform to POSIX.1-2008 .
 178 .Sh HISTORY
 179 The
 180 .Fn readlink
 181 function call appeared in
 182 .Bx 4.2 .
 183 The
 184 .Fn readlinkat
 185 system call appeared in OS X 10.10