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 2017-09-15 "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 .PP
  39 .BI "char *getcwd(char *" buf ", size_t " size );
  40 .PP
  41 .BI "char *getwd(char *" buf );
  42 .PP
  43 .B "char *get_current_dir_name(void);"
  44 .fi
  45 .PP
  46 .in -4n
  47 Feature Test Macro Requirements for glibc (see
  48 .BR feature_test_macros (7)):
  49 .in
  50 .PP
  51 .BR get_current_dir_name ():
  52 .RS
  53 _GNU_SOURCE
  54 .RE
  55 .PP
  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 .PP
  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 This is no longer true under some C libraries; see
  96 .BR NOTES .
  97 .PP
  98 The
  99 .BR getcwd ()
 100 function copies an absolute pathname of the current working directory
 101 to the array pointed to by
 102 .IR buf ,
 103 which is of length
 104 .IR size .
 105 .PP
 106 If the length of the absolute pathname of the current working directory,
 107 including the terminating null byte, exceeds
 108 .I size
 109 bytes, NULL is returned, and
 110 .I errno
 111 is set to
 112 .BR ERANGE ;
 113 an application should check for this error, and allocate a larger
 114 buffer if necessary.
 115 .PP
 116 As an extension to the POSIX.1-2001 standard, glibc's
 117 .BR getcwd ()
 118 allocates the buffer dynamically using
 119 .BR malloc (3)
 120 if
 121 .I buf
 122 is NULL.
 123 In this case, the allocated buffer has the length
 124 .I size
 125 unless
 126 .I size
 127 is zero, when
 128 .I buf
 129 is allocated as big as necessary.
 130 The caller should
 131 .BR free (3)
 132 the returned buffer.
 133 .PP
 134 .BR get_current_dir_name ()
 135 will
 136 .BR malloc (3)
 137 an array big enough to hold the absolute pathname of
 138 the current working directory.
 139 If the environment
 140 variable
 141 .B PWD
 142 is set, and its value is correct, then that value will be returned.
 143 The caller should
 144 .BR free (3)
 145 the returned buffer.
 146 .PP
 147 .BR getwd ()
 148 does not
 149 .BR malloc (3)
 150 any memory.
 151 The
 152 .I buf
 153 argument should be a pointer to an array at least
 154 .B PATH_MAX
 155 bytes long.
 156 If the length of the absolute pathname of the current working directory,
 157 including the terminating null byte, exceeds
 158 .B PATH_MAX
 159 bytes, NULL is returned, and
 160 .I errno
 161 is set to
 162 .BR ENAMETOOLONG .
 163 (Note that on some systems,
 164 .B PATH_MAX
 165 may not be a compile-time constant;
 166 furthermore, its value may depend on the filesystem, see
 167 .BR pathconf (3).)
 168 For portability and security reasons, use of
 169 .BR getwd ()
 170 is deprecated.
 171 .SH RETURN VALUE
 172 On success, these functions return a pointer to a string containing
 173 the pathname of the current working directory.
 174 In the case
 175 .BR getcwd ()
 176 and
 177 .BR getwd ()
 178 this is the same value as
 179 .IR buf .
 180 .PP
 181 On failure, these functions return NULL, and
 182 .I errno
 183 is set to indicate the error.
 184 The contents of the array pointed to by
 185 .I buf
 186 are undefined on error.
 187 .SH ERRORS
 188 .TP
 189 .B EACCES
 190 Permission to read or search a component of the filename was denied.
 191 .TP
 192 .B EFAULT
 193 .I buf
 194 points to a bad address.
 195 .TP
 196 .B EINVAL
 197 The
 198 .I size
 199 argument is zero and
 200 .I buf
 201 is not a null pointer.
 202 .TP
 203 .B EINVAL
 204 .BR getwd ():
 205 .I buf
 206 is NULL.
 207 .TP
 208 .B ENAMETOOLONG
 209 .BR getwd ():
 210 The size of the null-terminated absolute pathname string exceeds
 211 .B PATH_MAX
 212 bytes.
 213 .TP
 214 .B ENOENT
 215 The current working directory has been unlinked.
 216 .TP
 217 .B ENOMEM
 218 Out of memory.
 219 .TP
 220 .B ERANGE
 221 The
 222 .I size
 223 argument is less than the length of the absolute pathname of the
 224 working directory, including the terminating null byte.
 225 You need to allocate a bigger array and try again.
 226 .SH ATTRIBUTES
 227 For an explanation of the terms used in this section, see
 228 .BR attributes (7).
 229 .TS
 230 allbox;
 231 lbw22 lb lb
 232 l l l.
 233 Interface       Attribute       Value
 234 T{
 235 .BR getcwd (),
 236 .BR getwd ()
 237 T}      Thread safety   MT-Safe
 238 T{
 239 .BR get_current_dir_name ()
 240 T}      Thread safety   MT-Safe env
 241 .TE
 242 .SH CONFORMING TO
 243 .BR getcwd ()
 244 conforms to POSIX.1-2001.
 245 Note however that POSIX.1-2001 leaves the behavior of
 246 .BR getcwd ()
 247 unspecified if
 248 .I buf
 249 is NULL.
 250 .PP
 251 .BR getwd ()
 252 is present in POSIX.1-2001, but marked LEGACY.
 253 POSIX.1-2008 removes the specification of
 254 .BR getwd ().
 255 Use
 256 .BR getcwd ()
 257 instead.
 258 POSIX.1-2001
 259 does not define any errors for
 260 .BR getwd ().
 261 .PP
 262 .BR get_current_dir_name ()
 263 is a GNU extension.
 264 .SH NOTES
 265 Under Linux, the function
 266 .BR getcwd ()
 267 is a system call (since 2.1.92).
 268 On older systems it would query
 269 .IR /proc/self/cwd .
 270 If both system call and proc filesystem are missing, a
 271 generic implementation is called.
 272 Only in that case can
 273 these calls fail under Linux with
 274 .BR EACCES .
 275 .PP
 276 Since a Linux 2.6.36 change that added "(unreachable)", the glibc
 277 .BR getcwd ()
 278 has failed to conform to POSIX and returned a relative path when the API
 279 contract requires an absolute path.
 280 With glibc 2.27 onwards this is corrected;
 281 calling
 282 .BR getcwd ()
 283 from such a path will now result in failure with
 284 .BR ENOENT .
 285 .PP
 286 These functions are often used to save the location of the current working
 287 directory for the purpose of returning to it later.
 288 Opening the current
 289 directory (".") and calling
 290 .BR fchdir (2)
 291 to return is usually a faster and more reliable alternative when sufficiently
 292 many file descriptors are available, especially on platforms other than Linux.
 293 .SH SEE ALSO
 294 .BR pwd (1),
 295 .BR chdir (2),
 296 .BR fchdir (2),
 297 .BR open (2),
 298 .BR unlink (2),
 299 .BR free (3),
 300 .BR malloc (3)