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 .Sh RETURN VALUES
  89 The call returns the count of characters placed in the buffer
  90 if it succeeds, or a -1 if an error occurs, placing the error
  91 code in the global variable
  92 .Va errno .
  93 .Sh ERRORS
  94 .Fn readlink
  95 will fail if:
  96 .Bl -tag -width Er
  97 .\" ===========
  98 .It Bq Er EACCES
  99 Search permission is denied for a component of the path prefix.
 100 .\" ===========
 101 .It Bq Er EFAULT
 102 .Fa Buf
 103 extends outside the process's allocated address space.
 104 .\" ===========
 105 .It Bq Er EINVAL
 106 The named file is not a symbolic link.
 107 .\" ===========
 108 .It Bq Er EIO
 109 An I/O error occurred while reading from the file system.
 110 .\" ===========
 111 .It Bq Er ELOOP
 112 Too many symbolic links are encountered in translating the pathname.
 113 This is taken to be indicative of a looping symbolic link.
 114 .\" ===========
 115 .It Bq Er ENAMETOOLONG
 116 A component of a pathname exceeded
 117 .Dv {NAME_MAX}
 118 characters, or an entire path name
 119 (possibly expanded by a symbolic link) exceeded
 120 .Dv {PATH_MAX}
 121 characters.
 122 .\" ===========
 123 .It Bq Er ENOENT
 124 The named file does not exist.
 125 .\" ===========
 126 .It Bq Er ENOTDIR
 127 A component of the path prefix is not a directory.
 128 .El
 129 .Pp
 130 In addition to the errors returned by the
 131 .Fn readlink ,
 132 the
 133 .Fn readlinkat
 134 may fail if:
 135 .Bl -tag -width Er
 136 .It Bq Er EBADF
 137 The
 138 .Fa path
 139 argument does not specify an absolute path and the
 140 .Fa fd
 141 argument is neither
 142 .Dv AT_FDCWD
 143 nor a valid file descriptor open for searching.
 144 .It Bq Er ENOTDIR
 145 The
 146 .Fa path
 147 argument is not an absolute path and
 148 .Fa fd
 149 is neither
 150 .Dv AT_FDCWD
 151 nor a file descriptor associated with a directory.
 152 .El
 153 .Sh LEGACY SYNOPSIS
 154 .Fd #include <unistd.h>
 155 .Pp
 156 .Ft int
 157 .br
 158 .Fo readlink
 159 .Fa "const char *path"
 160 .Fa "char *buf"
 161 .Fa "int bufsize"
 162 .Fc ;
 163 .Pp
 164 The function type and the type of
 165 .Fa bufsize
 166 have changed.
 167 .Sh SEE ALSO
 168 .Xr lstat 2 ,
 169 .Xr stat 2 ,
 170 .Xr symlink 2 ,
 171 .Xr compat 5 ,
 172 .Xr symlink 7
 173 .Sh STANDARDS
 174 The
 175 .Fn readlinkat
 176 system call is expected to conform to POSIX.1-2008 .
 177 .Sh HISTORY
 178 The
 179 .Fn readlink
 180 function call appeared in
 181 .Bx 4.2 .
 182 The
 183 .Fn readlinkat
 184 system call appeared in OS X 10.10