man3/getcwd.3

   1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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  25 .\" Modified Wed Jul 21 22:35:42 1993 by Rik Faith (faith@cs.unc.edu)
  26 .\" Modified 18 Mar 1996 by Martin Schulze (joey@infodrom.north.de):
  27 .\"   Corrected description of getwd().
  28 .\" Modified Sat Aug 21 12:32:12 MET 1999 by aeb - applied fix by aj
  29 .\" Modified Mon Dec 11 13:32:51 MET 2000 by aeb
  30 .\" Modified Thu Apr 22 03:49:15 CEST 2002 by Roger Luethi <rl@hellgate.ch>
  31 .\"
  32 .TH GETCWD 3 2015-04-19 "GNU" "Linux Programmer's Manual"
  33 .SH NAME
  34 getcwd, getwd, get_current_dir_name \- get current working directory
  35 .SH SYNOPSIS
  36 .nf
  37 .B #include <unistd.h>
  38 .sp
  39 .BI "char *getcwd(char *" buf ", size_t " size );
  40 .sp
  41 .BI "char *getwd(char *" buf );
  42 .sp
  43 .B "char *get_current_dir_name(void);"
  44 .fi
  45 .sp
  46 .in -4n
  47 Feature Test Macro Requirements for glibc (see
  48 .BR feature_test_macros (7)):
  49 .sp
  50 .in
  51 .BR get_current_dir_name ():
  52 .RS
  53 _GNU_SOURCE
  54 .RE
  55 .sp
  56 .BR getwd ():
  57 .ad l
  58 .RS 4
  59 .PD 0
  60 .TP 4
  61 Since glibc 2.12:
  62 .nf
  63 _BSD_SOURCE ||
  64     (_XOPEN_SOURCE\ >=\ 500 ||
  65         _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED) &&
  66     !(_POSIX_C_SOURCE\ >=\ 200809L || _XOPEN_SOURCE\ >=\ 700)
  67 .TP 4
  68 .fi
  69 Before glibc 2.12:
  70 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  71 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  72 .PD
  73 .RE
  74 .ad b
  75 .SH DESCRIPTION
  76 These functions return a null-terminated string containing an
  77 absolute pathname that is the current working directory of
  78 the calling process.
  79 The pathname is returned as the function result and via the argument
  80 .IR buf ,
  81 if present.
  82
  83 If the current directory is not below the root directory of the current
  84 process (e.g., because the process set a new filesystem root using
  85 .BR chroot (2)
  86 without changing its current directory into the new root),
  87 then, since Linux 2.6.36,
  88 .\" commit 8df9d1a4142311c084ffeeacb67cd34d190eff74
  89 the returned path will be prefixed with the string "(unreachable)".
  90 Such behavior can also be caused by an unprivileged user by changing
  91 the current directory into another mount namespace.
  92 When dealing with paths from untrusted sources, callers of these
  93 functions should consider checking whether the returned path starts
  94 with '/' or '(' to avoid misinterpreting an unreachable path
  95 as a relative path.
  96
  97 The
  98 .BR getcwd ()
  99 function copies an absolute pathname of the current working directory
 100 to the array pointed to by
 101 .IR buf ,
 102 which is of length
 103 .IR size .
 104 .PP
 105 If the length of the absolute pathname of the current working directory,
 106 including the terminating null byte, exceeds
 107 .I size
 108 bytes, NULL is returned, and
 109 .I errno
 110 is set to
 111 .BR ERANGE ;
 112 an application should check for this error, and allocate a larger
 113 buffer if necessary.
 114 .PP
 115 As an extension to the POSIX.1-2001 standard, glibc's
 116 .BR getcwd ()
 117 allocates the buffer dynamically using
 118 .BR malloc (3)
 119 if
 120 .I buf
 121 is NULL.
 122 In this case, the allocated buffer has the length
 123 .I size
 124 unless
 125 .I size
 126 is zero, when
 127 .I buf
 128 is allocated as big as necessary.
 129 The caller should
 130 .BR free (3)
 131 the returned buffer.
 132
 133 .BR get_current_dir_name ()
 134 will
 135 .BR malloc (3)
 136 an array big enough to hold the absolute pathname of
 137 the current working directory.
 138 If the environment
 139 variable
 140 .B PWD
 141 is set, and its value is correct, then that value will be returned.
 142 The caller should
 143 .BR free (3)
 144 the returned buffer.
 145
 146 .BR getwd ()
 147 does not
 148 .BR malloc (3)
 149 any memory.
 150 The
 151 .I buf
 152 argument should be a pointer to an array at least
 153 .B PATH_MAX
 154 bytes long.
 155 If the length of the absolute pathname of the current working directory,
 156 including the terminating null byte, exceeds
 157 .B PATH_MAX
 158 bytes, NULL is returned, and
 159 .I errno
 160 is set to
 161 .BR ENAMETOOLONG .
 162 (Note that on some systems,
 163 .B PATH_MAX
 164 may not be a compile-time constant;
 165 furthermore, its value may depend on the filesystem, see
 166 .BR pathconf (3).)
 167 For portability and security reasons, use of
 168 .BR getwd ()
 169 is deprecated.
 170 .SH RETURN VALUE
 171 On success, these functions return a pointer to a string containing
 172 the pathname of the current working directory.
 173 In the case
 174 .BR getcwd ()
 175 and
 176 .BR getwd ()
 177 this is the same value as
 178 .IR buf .
 179
 180 On failure, these functions return NULL, and
 181 .I errno
 182 is set to indicate the error.
 183 The contents of the array pointed to by
 184 .I buf
 185 are undefined on error.
 186 .SH ERRORS
 187 .TP
 188 .B EACCES
 189 Permission to read or search a component of the filename was denied.
 190 .TP
 191 .B EFAULT
 192 .I buf
 193 points to a bad address.
 194 .TP
 195 .B EINVAL
 196 The
 197 .I size
 198 argument is zero and
 199 .I buf
 200 is not a null pointer.
 201 .TP
 202 .B EINVAL
 203 .BR getwd ():
 204 .I buf
 205 is NULL.
 206 .TP
 207 .B ENAMETOOLONG
 208 .BR getwd ():
 209 The size of the null-terminated absolute pathname string exceeds
 210 .B PATH_MAX
 211 bytes.
 212 .TP
 213 .B ENOMEM
 214 Out of memory.
 215 .TP
 216 .B ENOENT
 217 The current working directory has been unlinked.
 218 .TP
 219 .B ERANGE
 220 The
 221 .I size
 222 argument is less than the length of the absolute pathname of the
 223 working directory, including the terminating null byte.
 224 You need to allocate a bigger array and try again.
 225 .SH ATTRIBUTES
 226 For an explanation of the terms used in this section, see
 227 .BR attributes (7).
 228 .TS
 229 allbox;
 230 lbw22 lb lb
 231 l l l.
 232 Interface       Attribute       Value
 233 T{
 234 .BR getcwd (),
 235 .BR getwd ()
 236 T}      Thread safety   MT-Safe
 237 T{
 238 .BR get_current_dir_name ()
 239 T}      Thread safety   MT-Safe env
 240 .TE
 241 .SH CONFORMING TO
 242 .BR getcwd ()
 243 conforms to POSIX.1-2001.
 244 Note however that POSIX.1-2001 leaves the behavior of
 245 .BR getcwd ()
 246 unspecified if
 247 .I buf
 248 is NULL.
 249
 250 .BR getwd ()
 251 is present in POSIX.1-2001, but marked LEGACY.
 252 POSIX.1-2008 removes the specification of
 253 .BR getwd ().
 254 Use
 255 .BR getcwd ()
 256 instead.
 257 POSIX.1-2001
 258 does not define any errors for
 259 .BR getwd ().
 260
 261 .BR get_current_dir_name ()
 262 is a GNU extension.
 263 .SH NOTES
 264 Under Linux, the function
 265 .BR getcwd ()
 266 is a system call (since 2.1.92).
 267 On older systems it would query
 268 .IR /proc/self/cwd .
 269 If both system call and proc filesystem are missing, a
 270 generic implementation is called.
 271 Only in that case can
 272 these calls fail under Linux with
 273 .BR EACCES .
 274 .LP
 275 These functions are often used to save the location of the current working
 276 directory for the purpose of returning to it later.
 277 Opening the current
 278 directory (".") and calling
 279 .BR fchdir (2)
 280 to return is usually a faster and more reliable alternative when sufficiently
 281 many file descriptors are available, especially on platforms other than Linux.
 282 .SH SEE ALSO
 283 .BR chdir (2),
 284 .BR fchdir (2),
 285 .BR open (2),
 286 .BR unlink (2),
 287 .BR free (3),
 288 .BR malloc (3)