man3/scandir.3

   1 .\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified Sat Jul 24 18:26:16 1993 by Rik Faith (faith@cs.unc.edu)
  30 .\" Modified Thu Apr 11 17:11:33 1996 by Andries Brouwer (aeb@cwi.nl):
  31 .\"     Corrected type of compar routines, as suggested by
  32 .\"     Miguel Barreiro (enano@avalon.yaix.es).  Added example.
  33 .\" Modified Sun Sep 24 20:15:46 2000 by aeb, following Petter Reinholdtsen.
  34 .\" Modified 2001-12-26 by aeb, following Joey. Added versionsort.
  35 .\"
  36 .\" The pieces on scandirat(3) were copyright and licensed as follows.
  37 .\"
  38 .\" Copyright (c) 2012, Mark R. Bannister <cambridge@users.sourceforge.net>
  39 .\"        based on text in mkfifoat.3 Copyright (c) 2006, Michael Kerrisk
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  61 .\"
  62 .TH SCANDIR 3  2017-09-15 "GNU" "Linux Programmer's Manual"
  63 .SH NAME
  64 scandir, scandirat, alphasort, versionsort \- scan
  65 a directory for matching entries
  66 .SH SYNOPSIS
  67 .nf
  68 .B #include <dirent.h>
  69 .PP
  70 .BI "int scandir(const char *" dirp ", struct dirent ***" namelist ,
  71 .RS
  72 .BI "int (*" filter ")(const struct dirent *),"
  73 .BI "int (*" compar ")(const struct dirent **, const struct dirent **));"
  74 .RE
  75 .PP
  76 .BI "int alphasort(const struct dirent **" a ", const struct dirent **" b );
  77 .PP
  78 .BI "int versionsort(const struct dirent **" a ", const struct dirent **" b );
  79
  80 .BR "#include <fcntl.h>" "          /* Definition of AT_* constants */"
  81 .B #include <dirent.h>
  82 .PP
  83 .fi
  84 .BI "int scandirat(int " dirfd ", const char *" dirp ","
  85 .BI "struct dirent ***" namelist ,
  86 .nf
  87 .RS
  88 .BI "int (*" filter ")(const struct dirent *),"
  89 .BI "int (*" compar ")(const struct dirent **, const struct dirent **));"
  90 .RE
  91 .fi
  92 .PP
  93 .in -4n
  94 Feature Test Macro Requirements for glibc (see
  95 .BR feature_test_macros (7)):
  96 .in
  97 .PP
  98 .BR scandir (),
  99 .BR alphasort ():
 100 .br
 101 .RS 4
 102 .PD 0
 103 .ad b
 104 /* Since glibc 2.10: */ _POSIX_C_SOURCE\ >=\ 200809L
 105     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
 106 .PD
 107 .RE
 108 .PP
 109 .BR versionsort ():
 110 _GNU_SOURCE
 111 .PP
 112 .BR scandirat ():
 113 _GNU_SOURCE
 114 .SH DESCRIPTION
 115 The
 116 .BR scandir ()
 117 function scans the directory \fIdirp\fP, calling
 118 \fIfilter\fP() on each directory entry.
 119 Entries for which
 120 \fIfilter\fP() returns nonzero are stored in strings allocated via
 121 .BR malloc (3),
 122 sorted using
 123 .BR qsort (3)
 124 with the comparison
 125 function \fIcompar\fP(), and collected in array \fInamelist\fP
 126 which is allocated via
 127 .BR malloc (3).
 128 If \fIfilter\fP is NULL, all entries are selected.
 129 .PP
 130 The
 131 .BR alphasort ()
 132 and
 133 .BR versionsort ()
 134 functions can be used as the comparison function
 135 .IR compar ().
 136 The former sorts directory entries using
 137 .BR strcoll (3),
 138 the latter using
 139 .BR strverscmp (3)
 140 on the strings \fI(*a)\->d_name\fP and \fI(*b)\->d_name\fP.
 141 .SS scandirat()
 142 The
 143 .BR scandirat ()
 144 function operates in exactly the same way as
 145 .BR scandir (),
 146 except for the differences described here.
 147 .PP
 148 If the pathname given in
 149 .I dirp
 150 is relative, then it is interpreted relative to the directory
 151 referred to by the file descriptor
 152 .I dirfd
 153 (rather than relative to the current working directory of
 154 the calling process, as is done by
 155 .BR scandir ()
 156 for a relative pathname).
 157 .PP
 158 If
 159 .I dirp
 160 is relative and
 161 .I dirfd
 162 is the special value
 163 .BR AT_FDCWD ,
 164 then
 165 .I dirp
 166 is interpreted relative to the current working
 167 directory of the calling process (like
 168 .BR scandir ()).
 169 .PP
 170 If
 171 .I dirp
 172 is absolute, then
 173 .I dirfd
 174 is ignored.
 175 .PP
 176 See
 177 .BR openat (2)
 178 for an explanation of the need for
 179 .BR scandirat ().
 180 .SH RETURN VALUE
 181 The
 182 .BR scandir ()
 183 function returns the number of directory entries
 184 selected.
 185 On error, \-1 is returned, with
 186 .I errno
 187 set to indicate the cause of the error.
 188 .PP
 189 The
 190 .BR alphasort ()
 191 and
 192 .BR versionsort ()
 193 functions return an integer less than, equal to,
 194 or greater than zero if the first argument is considered to be
 195 respectively less than, equal to, or greater than the second.
 196 .SH ERRORS
 197 .TP
 198 .B ENOENT
 199 The path in \fIdirp\fR does not exist.
 200 .TP
 201 .B ENOMEM
 202 Insufficient memory to complete the operation.
 203 .TP
 204 .B ENOTDIR
 205 The path in \fIdirp\fR is not a directory.
 206 .PP
 207 The following additional errors can occur for
 208 .BR scandirat ():
 209 .TP
 210 .B EBADF
 211 .I dirfd
 212 is not a valid file descriptor.
 213 .TP
 214 .B ENOTDIR
 215 .I dirp
 216 is a relative path and
 217 .I dirfd
 218 is a file descriptor referring to a file other than a directory.
 219 .SH VERSIONS
 220 .BR versionsort ()
 221 was added to glibc in version 2.1.
 222 .PP
 223 .BR scandirat ()
 224 was added to glibc in version 2.15.
 225 .SH ATTRIBUTES
 226 For an explanation of the terms used in this section, see
 227 .BR attributes (7).
 228 .TS
 229 allbox;
 230 lbw26 lb lb
 231 l l l.
 232 Interface       Attribute       Value
 233 T{
 234 .BR scandir (),
 235 .BR scandirat ()
 236 T}      Thread safety   MT-Safe
 237 T{
 238 .BR alphasort (),
 239 .BR versionsort ()
 240 T}      Thread safety   MT-Safe locale
 241 .TE
 242 .sp 1
 243 .SH CONFORMING TO
 244 .BR alphasort (),
 245 .BR scandir ():
 246 4.3BSD, POSIX.1-2008.
 247 .PP
 248 .BR versionsort ()
 249 and
 250 .BR scandirat ()
 251 are GNU extensions.
 252 .\" .LP
 253 .\" The functions
 254 .\" .BR scandir ()
 255 .\" and
 256 .\" .BR alphasort ()
 257 .\" are from 4.3BSD, and have been available under Linux since libc4.
 258 .\" Libc4 and libc5 use the more precise prototype
 259 .\" .sp
 260 .\" .nf
 261 .\"    int alphasort(const struct dirent ** a,
 262 .\"                  const struct dirent **b);
 263 .\" .fi
 264 .\" .sp
 265 .\" but glibc 2.0 returns to the imprecise BSD prototype.
 266 .SH NOTES
 267 Since glibc 2.1,
 268 .BR alphasort ()
 269 calls
 270 .BR strcoll (3);
 271 earlier it used
 272 .BR strcmp (3).
 273 .PP
 274 Before glibc 2.10, the two arguments of
 275 .BR alphasort ()
 276 and
 277 .BR versionsort ()
 278 were typed as
 279 .IR "const void\ *" .
 280 When
 281 .BR alphasort ()
 282 was standardized in POSIX.1-2008,
 283 the argument type was specified as the type-safe
 284 .IR "const struct dirent\ **",
 285 and glibc 2.10 changed the definition of
 286 .BR alphasort ()
 287 (and the nonstandard
 288 .BR versionsort ())
 289 to match the standard.
 290 .SH EXAMPLE
 291 The program below prints a list of the files in the current directory
 292 in reverse order.
 293 .\"
 294 .SS Program source
 295 \&
 296 .EX
 297 #define _DEFAULT_SOURCE
 298 #include <dirent.h>
 299 #include <stdio.h>
 300 #include <stdlib.h>
 301
 302 int
 303 main(void)
 304 {
 305     struct dirent **namelist;
 306     int n;
 307
 308     n = scandir(".", &namelist, NULL, alphasort);
 309     if (n == -1) {
 310         perror("scandir");
 311         exit(EXIT_FAILURE);
 312     }
 313
 314     while (n\-\-) {
 315         printf("%s\en", namelist[n]\->d_name);
 316         free(namelist[n]);
 317     }
 318     free(namelist);
 319
 320     exit(EXIT_SUCCESS);
 321 }
 322 .EE
 323 .SH SEE ALSO
 324 .BR closedir (3),
 325 .BR fnmatch (3),
 326 .BR opendir (3),
 327 .BR readdir (3),
 328 .BR rewinddir (3),
 329 .BR seekdir (3),
 330 .BR strcmp (3),
 331 .BR strcoll (3),
 332 .BR strverscmp (3),
 333 .BR telldir (3)