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 (_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
  64     || /* Glibc since 2.19: */ _DEFAULT_SOURCE
  65     || /* Glibc versions <= 2.19: */ _BSD_SOURCE
  66 .TP 4
  67 .fi
  68 Before glibc 2.12:
  69 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
  70 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  71 .PD
  72 .RE
  73 .ad b
  74 .SH DESCRIPTION
  75 These functions return a null-terminated string containing an
  76 absolute pathname that is the current working directory of
  77 the calling process.
  78 The pathname is returned as the function result and via the argument
  79 .IR buf ,
  80 if present.
  81
  82 If the current directory is not below the root directory of the current
  83 process (e.g., because the process set a new filesystem root using
  84 .BR chroot (2)
  85 without changing its current directory into the new root),
  86 then, since Linux 2.6.36,
  87 .\" commit 8df9d1a4142311c084ffeeacb67cd34d190eff74
  88 the returned path will be prefixed with the string "(unreachable)".
  89 Such behavior can also be caused by an unprivileged user by changing
  90 the current directory into another mount namespace.
  91 When dealing with paths from untrusted sources, callers of these
  92 functions should consider checking whether the returned path starts
  93 with '/' or '(' to avoid misinterpreting an unreachable path
  94 as a relative path.
  95
  96 The
  97 .BR getcwd ()
  98 function copies an absolute pathname of the current working directory
  99 to the array pointed to by
 100 .IR buf ,
 101 which is of length
 102 .IR size .
 103 .PP
 104 If the length of the absolute pathname of the current working directory,
 105 including the terminating null byte, exceeds
 106 .I size
 107 bytes, NULL is returned, and
 108 .I errno
 109 is set to
 110 .BR ERANGE ;
 111 an application should check for this error, and allocate a larger
 112 buffer if necessary.
 113 .PP
 114 As an extension to the POSIX.1-2001 standard, glibc's
 115 .BR getcwd ()
 116 allocates the buffer dynamically using
 117 .BR malloc (3)
 118 if
 119 .I buf
 120 is NULL.
 121 In this case, the allocated buffer has the length
 122 .I size
 123 unless
 124 .I size
 125 is zero, when
 126 .I buf
 127 is allocated as big as necessary.
 128 The caller should
 129 .BR free (3)
 130 the returned buffer.
 131
 132 .BR get_current_dir_name ()
 133 will
 134 .BR malloc (3)
 135 an array big enough to hold the absolute pathname of
 136 the current working directory.
 137 If the environment
 138 variable
 139 .B PWD
 140 is set, and its value is correct, then that value will be returned.
 141 The caller should
 142 .BR free (3)
 143 the returned buffer.
 144
 145 .BR getwd ()
 146 does not
 147 .BR malloc (3)
 148 any memory.
 149 The
 150 .I buf
 151 argument should be a pointer to an array at least
 152 .B PATH_MAX
 153 bytes long.
 154 If the length of the absolute pathname of the current working directory,
 155 including the terminating null byte, exceeds
 156 .B PATH_MAX
 157 bytes, NULL is returned, and
 158 .I errno
 159 is set to
 160 .BR ENAMETOOLONG .
 161 (Note that on some systems,
 162 .B PATH_MAX
 163 may not be a compile-time constant;
 164 furthermore, its value may depend on the filesystem, see
 165 .BR pathconf (3).)
 166 For portability and security reasons, use of
 167 .BR getwd ()
 168 is deprecated.
 169 .SH RETURN VALUE
 170 On success, these functions return a pointer to a string containing
 171 the pathname of the current working directory.
 172 In the case
 173 .BR getcwd ()
 174 and
 175 .BR getwd ()
 176 this is the same value as
 177 .IR buf .
 178
 179 On failure, these functions return NULL, and
 180 .I errno
 181 is set to indicate the error.
 182 The contents of the array pointed to by
 183 .I buf
 184 are undefined on error.
 185 .SH ERRORS
 186 .TP
 187 .B EACCES
 188 Permission to read or search a component of the filename was denied.
 189 .TP
 190 .B EFAULT
 191 .I buf
 192 points to a bad address.
 193 .TP
 194 .B EINVAL
 195 The
 196 .I size
 197 argument is zero and
 198 .I buf
 199 is not a null pointer.
 200 .TP
 201 .B EINVAL
 202 .BR getwd ():
 203 .I buf
 204 is NULL.
 205 .TP
 206 .B ENAMETOOLONG
 207 .BR getwd ():
 208 The size of the null-terminated absolute pathname string exceeds
 209 .B PATH_MAX
 210 bytes.
 211 .TP
 212 .B ENOMEM
 213 Out of memory.
 214 .TP
 215 .B ENOENT
 216 The current working directory has been unlinked.
 217 .TP
 218 .B ERANGE
 219 The
 220 .I size
 221 argument is less than the length of the absolute pathname of the
 222 working directory, including the terminating null byte.
 223 You need to allocate a bigger array and try again.
 224 .SH ATTRIBUTES
 225 For an explanation of the terms used in this section, see
 226 .BR attributes (7).
 227 .TS
 228 allbox;
 229 lbw22 lb lb
 230 l l l.
 231 Interface       Attribute       Value
 232 T{
 233 .BR getcwd (),
 234 .BR getwd ()
 235 T}      Thread safety   MT-Safe
 236 T{
 237 .BR get_current_dir_name ()
 238 T}      Thread safety   MT-Safe env
 239 .TE
 240 .SH CONFORMING TO
 241 .BR getcwd ()
 242 conforms to POSIX.1-2001.
 243 Note however that POSIX.1-2001 leaves the behavior of
 244 .BR getcwd ()
 245 unspecified if
 246 .I buf
 247 is NULL.
 248
 249 .BR getwd ()
 250 is present in POSIX.1-2001, but marked LEGACY.
 251 POSIX.1-2008 removes the specification of
 252 .BR getwd ().
 253 Use
 254 .BR getcwd ()
 255 instead.
 256 POSIX.1-2001
 257 does not define any errors for
 258 .BR getwd ().
 259
 260 .BR get_current_dir_name ()
 261 is a GNU extension.
 262 .SH NOTES
 263 Under Linux, the function
 264 .BR getcwd ()
 265 is a system call (since 2.1.92).
 266 On older systems it would query
 267 .IR /proc/self/cwd .
 268 If both system call and proc filesystem are missing, a
 269 generic implementation is called.
 270 Only in that case can
 271 these calls fail under Linux with
 272 .BR EACCES .
 273 .LP
 274 These functions are often used to save the location of the current working
 275 directory for the purpose of returning to it later.
 276 Opening the current
 277 directory (".") and calling
 278 .BR fchdir (2)
 279 to return is usually a faster and more reliable alternative when sufficiently
 280 many file descriptors are available, especially on platforms other than Linux.
 281 .SH SEE ALSO
 282 .BR pwd (1),
 283 .BR chdir (2),
 284 .BR fchdir (2),
 285 .BR open (2),
 286 .BR unlink (2),
 287 .BR free (3),
 288 .BR malloc (3)