1FTS(3) Linux Programmer's Manual FTS(3)
2
6 fts, fts_open, fts_read, fts_children, fts_set, fts_close - traverse a
7 file hierarchy
8
10 #include <sys/types.h>
11 #include <sys/stat.h>
12 #include <fts.h>
13 FTS *fts_open(char * const *path_argv, int options,
15 int (*compar)(const FTSENT **, const FTSENT **));
16 FTSENT *fts_read(FTS *ftsp);
18 FTSENT *fts_children(FTS *ftsp, int instr);
20 int fts_set(FTS *ftsp, FTSENT *f, int instr);
22 int fts_close(FTS *ftsp);
24
26 The fts functions are provided for traversing file hierarchies. A sim‐
27 ple overview is that the fts_open() function returns a "handle" (of
28 type FTS *) that refers to a file hierarchy "stream". This handle is
29 then supplied to the other fts functions. The function fts_read() re‐
30 turns a pointer to a structure describing one of the files in the file
31 hierarchy. The function fts_children() returns a pointer to a linked
32 list of structures, each of which describes one of the files contained
33 in a directory in the hierarchy.
34 In general, directories are visited two distinguishable times; in pre‐
36 order (before any of their descendants are visited) and in postorder
37 (after all of their descendants have been visited). Files are visited
38 once. It is possible to walk the hierarchy "logically" (visiting the
39 files that symbolic links point to) or physically (visiting the sym‐
40 bolic links themselves), order the walk of the hierarchy or prune
41 and/or revisit portions of the hierarchy.
42 Two structures (and associated types) are defined in the include file
44 <fts.h>. The first type is FTS, the structure that represents the file
45 hierarchy itself. The second type is FTSENT, the structure that repre‐
46 sents a file in the file hierarchy. Normally, an FTSENT structure is
47 returned for every file in the file hierarchy. In this manual page,
48 "file" and "FTSENT structure" are generally interchangeable.
49 The FTSENT structure contains fields describing a file. The structure
51 contains at least the following fields (there are additional fields
52 that should be considered private to the implementation):
53 typedef struct _ftsent {
55 unsigned short fts_info; /* flags for FTSENT structure */
56 char *fts_accpath; /* access path */
57 char *fts_path; /* root path */
58 short fts_pathlen; /* strlen(fts_path) +
59 strlen(fts_name) */
60 char *fts_name; /* filename */
61 short fts_namelen; /* strlen(fts_name) */
62 short fts_level; /* depth (-1 to N) */
63 int fts_errno; /* file errno */
64 long fts_number; /* local numeric value */
65 void *fts_pointer; /* local address value */
66 struct _ftsent *fts_parent; /* parent directory */
67 struct _ftsent *fts_link; /* next file structure */
68 struct _ftsent *fts_cycle; /* cycle structure */
69 struct stat *fts_statp; /* stat(2) information */
70 } FTSENT;
71 These fields are defined as follows:
73 fts_info
75 One of the following values describing the returned FTSENT
76 structure and the file it represents. With the exception of di‐
77 rectories without errors (FTS_D), all of these entries are ter‐
78 minal, that is, they will not be revisited, nor will any of
79 their descendants be visited.
80 FTS_D A directory being visited in preorder.
82 FTS_DC A directory that causes a cycle in the tree. (The
84 fts_cycle field of the FTSENT structure will be filled in
85 as well.)
86 FTS_DEFAULT
88 Any FTSENT structure that represents a file type not ex‐
89 plicitly described by one of the other fts_info values.
90 FTS_DNR
92 A directory which cannot be read. This is an error re‐
93 turn, and the fts_errno field will be set to indicate
94 what caused the error.
95 FTS_DOT
97 A file named "." or ".." which was not specified as a
98 filename to fts_open() (see FTS_SEEDOT).
99 FTS_DP A directory being visited in postorder. The contents of
101 the FTSENT structure will be unchanged from when it was
102 returned in preorder, that is, with the fts_info field
103 set to FTS_D.
104 FTS_ERR
106 This is an error return, and the fts_errno field will be
107 set to indicate what caused the error.
108 FTS_F A regular file.
110 FTS_NS A file for which no stat(2) information was available.
112 The contents of the fts_statp field are undefined. This
113 is an error return, and the fts_errno field will be set
114 to indicate what caused the error.
115 FTS_NSOK
117 A file for which no stat(2) information was requested.
118 The contents of the fts_statp field are undefined.
119 FTS_SL A symbolic link.
121 FTS_SLNONE
123 A symbolic link with a nonexistent target. The contents
124 of the fts_statp field reference the file characteristic
125 information for the symbolic link itself.
126 fts_accpath
128 A path for accessing the file from the current directory.
129 fts_path
131 The path for the file relative to the root of the traversal.
132 This path contains the path specified to fts_open() as a prefix.
133 fts_pathlen
135 The sum of the lengths of the strings referenced by fts_path and
136 fts_name.
137 fts_name
139 The name of the file.
140 fts_namelen
142 The length of the string referenced by fts_name.
143 fts_level
145 The depth of the traversal, numbered from -1 to N, where this
146 file was found. The FTSENT structure representing the parent of
147 the starting point (or root) of the traversal is numbered -1,
148 and the FTSENT structure for the root itself is numbered 0.
149 fts_errno
151 If fts_children() or fts_read() returns an FTSENT structure
152 whose fts_info field is set to FTS_DNR, FTS_ERR, or FTS_NS, the
153 fts_errno field contains the error number (i.e., the errno
154 value) specifying the cause of the error. Otherwise, the con‐
155 tents of the fts_errno field are undefined.
156 fts_number
158 This field is provided for the use of the application program
159 and is not modified by the fts functions. It is initialized to
160 0.
161 fts_pointer
163 This field is provided for the use of the application program
164 and is not modified by the fts functions. It is initialized to
165 NULL.
166 fts_parent
168 A pointer to the FTSENT structure referencing the file in the
169 hierarchy immediately above the current file, that is, the di‐
170 rectory of which this file is a member. A parent structure for
171 the initial entry point is provided as well, however, only the
172 fts_level, fts_number, and fts_pointer fields are guaranteed to
173 be initialized.
174 fts_link
176 Upon return from the fts_children() function, the fts_link field
177 points to the next structure in the NULL-terminated linked list
178 of directory members. Otherwise, the contents of the fts_link
179 field are undefined.
180 fts_cycle
182 If a directory causes a cycle in the hierarchy (see FTS_DC), ei‐
183 ther because of a hard link between two directories, or a sym‐
184 bolic link pointing to a directory, the fts_cycle field of the
185 structure will point to the FTSENT structure in the hierarchy
186 that references the same file as the current FTSENT structure.
187 Otherwise, the contents of the fts_cycle field are undefined.
188 fts_statp
190 A pointer to stat(2) information for the file.
191 A single buffer is used for all of the paths of all of the files in the
193 file hierarchy. Therefore, the fts_path and fts_accpath fields are
194 guaranteed to be null-terminated only for the file most recently re‐
195 turned by fts_read(). To use these fields to reference any files rep‐
196 resented by other FTSENT structures will require that the path buffer
197 be modified using the information contained in that FTSENT structure's
198 fts_pathlen field. Any such modifications should be undone before fur‐
199 ther calls to fts_read() are attempted. The fts_name field is always
200 null-terminated.
201 fts_open()
203 The fts_open() function takes a pointer to an array of character point‐
204 ers naming one or more paths which make up a logical file hierarchy to
205 be traversed. The array must be terminated by a null pointer.
206 There are a number of options, at least one of which (either FTS_LOGI‐
208 CAL or FTS_PHYSICAL) must be specified. The options are selected by
209 ORing the following values:
210 FTS_COMFOLLOW
212 This option causes any symbolic link specified as a root path to
213 be followed immediately whether or not FTS_LOGICAL is also spec‐
214 ified.
215 FTS_LOGICAL
217 This option causes the fts routines to return FTSENT structures
218 for the targets of symbolic links instead of the symbolic links
219 themselves. If this option is set, the only symbolic links for
220 which FTSENT structures are returned to the application are
221 those referencing nonexistent files. Either FTS_LOGICAL or
222 FTS_PHYSICAL must be provided to the fts_open() function.
223 FTS_NOCHDIR
225 As a performance optimization, the fts functions change directo‐
226 ries as they walk the file hierarchy. This has the side-effect
227 that an application cannot rely on being in any particular di‐
228 rectory during the traversal. The FTS_NOCHDIR option turns off
229 this optimization, and the fts functions will not change the
230 current directory. Note that applications should not themselves
231 change their current directory and try to access files unless
232 FTS_NOCHDIR is specified and absolute pathnames were provided as
233 arguments to fts_open().
234 FTS_NOSTAT
236 By default, returned FTSENT structures reference file character‐
237 istic information (the statp field) for each file visited. This
238 option relaxes that requirement as a performance optimization,
239 allowing the fts functions to set the fts_info field to FTS_NSOK
240 and leave the contents of the statp field undefined.
241 FTS_PHYSICAL
243 This option causes the fts routines to return FTSENT structures
244 for symbolic links themselves instead of the target files they
245 point to. If this option is set, FTSENT structures for all sym‐
246 bolic links in the hierarchy are returned to the application.
247 Either FTS_LOGICAL or FTS_PHYSICAL must be provided to the
248 fts_open() function.
249 FTS_SEEDOT
251 By default, unless they are specified as path arguments to
252 fts_open(), any files named "." or ".." encountered in the
253 file hierarchy are ignored. This option causes the fts routines
254 to return FTSENT structures for them.
255 FTS_XDEV
257 This option prevents fts from descending into directories that
258 have a different device number than the file from which the de‐
259 scent began.
260 The argument compar() specifies a user-defined function which may be
262 used to order the traversal of the hierarchy. It takes two pointers to
263 pointers to FTSENT structures as arguments and should return a negative
264 value, zero, or a positive value to indicate if the file referenced by
265 its first argument comes before, in any order with respect to, or af‐
266 ter, the file referenced by its second argument. The fts_accpath,
267 fts_path, and fts_pathlen fields of the FTSENT structures may never be
268 used in this comparison. If the fts_info field is set to FTS_NS or
269 FTS_NSOK, the fts_statp field may not either. If the compar() argument
270 is NULL, the directory traversal order is in the order listed in
271 path_argv for the root paths, and in the order listed in the directory
272 for everything else.
273 fts_read()
275 The fts_read() function returns a pointer to an FTSENT structure de‐
276 scribing a file in the hierarchy. Directories (that are readable and
277 do not cause cycles) are visited at least twice, once in preorder and
278 once in postorder. All other files are visited at least once. (Hard
279 links between directories that do not cause cycles or symbolic links to
280 symbolic links may cause files to be visited more than once, or direc‐
281 tories more than twice.)
282 If all the members of the hierarchy have been returned, fts_read() re‐
284 turns NULL and sets errno to 0. If an error unrelated to a file in the
285 hierarchy occurs, fts_read() returns NULL and sets errno to indicate
286 the error. If an error related to a returned file occurs, a pointer to
287 an FTSENT structure is returned, and errno may or may not have been set
288 (see fts_info).
289 The FTSENT structures returned by fts_read() may be overwritten after a
291 call to fts_close() on the same file hierarchy stream, or, after a call
292 to fts_read() on the same file hierarchy stream unless they represent a
293 file of type directory, in which case they will not be overwritten un‐
294 til after a call to fts_read() after the FTSENT structure has been re‐
295 turned by the function fts_read() in postorder.
296 fts_children()
298 The fts_children() function returns a pointer to an FTSENT structure
299 describing the first entry in a NULL-terminated linked list of the
300 files in the directory represented by the FTSENT structure most re‐
301 cently returned by fts_read(). The list is linked through the fts_link
302 field of the FTSENT structure, and is ordered by the user-specified
303 comparison function, if any. Repeated calls to fts_children() will re-
304 create this linked list.
305 As a special case, if fts_read() has not yet been called for a hierar‐
307 chy, fts_children() will return a pointer to the files in the logical
308 directory specified to fts_open(), that is, the arguments specified to
309 fts_open(). Otherwise, if the FTSENT structure most recently returned
310 by fts_read() is not a directory being visited in preorder, or the di‐
311 rectory does not contain any files, fts_children() returns NULL and
312 sets errno to zero. If an error occurs, fts_children() returns NULL
313 and sets errno to indicate the error.
314 The FTSENT structures returned by fts_children() may be overwritten af‐
316 ter a call to fts_children(), fts_close(), or fts_read() on the same
317 file hierarchy stream.
318 The instr argument is either zero or the following value:
320 FTS_NAMEONLY
322 Only the names of the files are needed. The contents of all the
323 fields in the returned linked list of structures are undefined
324 with the exception of the fts_name and fts_namelen fields.
325 fts_set()
327 The function fts_set() allows the user application to determine further
328 processing for the file f of the stream ftsp. The fts_set() function
329 returns 0 on success, and -1 if an error occurs.
330 The instr argument is either 0 (meaning "do nothing") or one of the
332 following values:
333 FTS_AGAIN
335 Revisit the file; any file type may be revisited. The next call
336 to fts_read() will return the referenced file. The fts_stat and
337 fts_info fields of the structure will be reinitialized at that
338 time, but no other fields will have been changed. This option
339 is meaningful only for the most recently returned file from
340 fts_read(). Normal use is for postorder directory visits, where
341 it causes the directory to be revisited (in both preorder and
342 postorder) as well as all of its descendants.
343 FTS_FOLLOW
345 The referenced file must be a symbolic link. If the referenced
346 file is the one most recently returned by fts_read(), the next
347 call to fts_read() returns the file with the fts_info and
348 fts_statp fields reinitialized to reflect the target of the sym‐
349 bolic link instead of the symbolic link itself. If the file is
350 one of those most recently returned by fts_children(), the
351 fts_info and fts_statp fields of the structure, when returned by
352 fts_read(), will reflect the target of the symbolic link instead
353 of the symbolic link itself. In either case, if the target of
354 the symbolic link does not exist, the fields of the returned
355 structure will be unchanged and the fts_info field will be set
356 to FTS_SLNONE.
357 If the target of the link is a directory, the preorder return,
359 followed by the return of all of its descendants, followed by a
360 postorder return, is done.
361 FTS_SKIP
363 No descendants of this file are visited. The file may be one of
364 those most recently returned by either fts_children() or
365 fts_read().
366 fts_close()
368 The fts_close() function closes the file hierarchy stream referred to
369 by ftsp and restores the current directory to the directory from which
370 fts_open() was called to open ftsp. The fts_close() function returns 0
371 on success, and -1 if an error occurs.
372
374 The function fts_open() may fail and set errno for any of the errors
375 specified for open(2) and malloc(3).
376 The function fts_close() may fail and set errno for any of the errors
378 specified for chdir(2) and close(2).
379 The functions fts_read() and fts_children() may fail and set errno for
381 any of the errors specified for chdir(2), malloc(3), opendir(3), read‐
382 dir(3), and stat(2).
383 In addition, fts_children(), fts_open(), and fts_set() may fail and set
385 errno as follows:
386 EINVAL options or instr was invalid.
388
390 These functions are available in Linux since glibc2.
391
393 For an explanation of the terms used in this section, see at‐
394 tributes(7).
395 ┌──────────────────────────────────────────┬───────────────┬───────────┐
397 │Interface │ Attribute │ Value │
398 ├──────────────────────────────────────────┼───────────────┼───────────┤
399 │fts_open(), fts_set(), fts_close() │ Thread safety │ MT-Safe │
400 ├──────────────────────────────────────────┼───────────────┼───────────┤
401 │fts_read(), fts_children() │ Thread safety │ MT-Unsafe │
402 └──────────────────────────────────────────┴───────────────┴───────────┘
403
405 4.4BSD.
406
408 In versions of glibc before 2.23, all of the APIs described in this man
409 page are not safe when compiling a program using the LFS APIs (e.g.,
410 when compiling with -D_FILE_OFFSET_BITS=64).
411
413 find(1), chdir(2), stat(2), ftw(3), qsort(3)
414
416 This page is part of release 5.12 of the Linux man-pages project. A
417 description of the project, information about reporting bugs, and the
418 latest version of this page, can be found at
419 https://www.kernel.org/doc/man-pages/.
420Linux 2021-03-22 FTS(3)