1FTS(3)                     Linux Programmer's Manual                    FTS(3)
2
3
4

NAME

6       fts,  fts_open, fts_read, fts_children, fts_set, fts_close - traverse a
7       file hierarchy
8

SYNOPSIS

10       #include <sys/types.h>
11       #include <sys/stat.h>
12       #include <fts.h>
13
14       FTS *fts_open(char * const *path_argv, int options,
15                     int (*compar)(const FTSENT **, const FTSENT **));
16
17       FTSENT *fts_read(FTS *ftsp);
18
19       FTSENT *fts_children(FTS *ftsp, int instr);
20
21       int fts_set(FTS *ftsp, FTSENT *f, int instr);
22
23       int fts_close(FTS *ftsp);
24

DESCRIPTION

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()
30       returns a pointer to a structure describing one of  the  files  in  the
31       file  hierarchy.   The  function  fts_children() returns a pointer to a
32       linked list of structures, each of which describes  one  of  the  files
33       contained in a directory in the hierarchy.
34
35       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
43       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
50       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
54           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
72       These fields are defined as follows:
73
74       fts_info    One of the following values describing the returned  FTSENT
75                   structure  and  the file it represents.  With the exception
76                   of directories without errors (FTS_D), all of these entries
77                   are terminal, that is, they will not be revisited, nor will
78                   any of their descendants be visited.
79
80                   FTS_D       A directory being visited in preorder.
81
82                   FTS_DC      A directory that causes a cycle  in  the  tree.
83                               (The  fts_cycle  field  of the FTSENT structure
84                               will be filled in as well.)
85
86                   FTS_DEFAULT Any FTSENT structure  that  represents  a  file
87                               type  not  explicitly  described  by one of the
88                               other fts_info values.
89
90                   FTS_DNR     A directory which cannot be read.  This  is  an
91                               error  return,  and the fts_errno field will be
92                               set to indicate what caused the error.
93
94                   FTS_DOT     A file named "."  or ".."  which was not speci‐
95                               fied  as a filename to fts_open() (see FTS_SEE‐
96                               DOT).
97
98                   FTS_DP      A directory being visited  in  postorder.   The
99                               contents   of  the  FTSENT  structure  will  be
100                               unchanged from when it  was  returned  in  pre‐
101                               order,  that is, with the fts_info field set to
102                               FTS_D.
103
104                   FTS_ERR     This is an  error  return,  and  the  fts_errno
105                               field  will  be set to indicate what caused the
106                               error.
107
108                   FTS_F       A regular file.
109
110                   FTS_NS      A file for which  no  stat(2)  information  was
111                               available.  The contents of the fts_statp field
112                               are undefined.  This is an  error  return,  and
113                               the  fts_errno  field  will  be set to indicate
114                               what caused the error.
115
116                   FTS_NSOK    A file for which  no  stat(2)  information  was
117                               requested.  The contents of the fts_statp field
118                               are undefined.
119
120                   FTS_SL      A symbolic link.
121
122                   FTS_SLNONE  A symbolic link with a nonexistent target.  The
123                               contents  of  the fts_statp field reference the
124                               file characteristic information  for  the  sym‐
125                               bolic link itself.
126
127       fts_accpath A path for accessing the file from the current directory.
128
129       fts_path    The  path  for the file relative to the root of the traver‐
130                   sal.  This path contains the path specified  to  fts_open()
131                   as a prefix.
132
133       fts_pathlen The  sum  of  the  lengths  of  the  strings  referenced by
134                   fts_path and fts_name.
135
136       fts_name    The name of the file.
137
138       fts_namelen The length of the string referenced by fts_name.
139
140       fts_level   The depth of the traversal, numbered from -1  to  N,  where
141                   this file was found.  The FTSENT structure representing the
142                   parent of the starting point (or root) of the traversal  is
143                   numbered  -1,  and the FTSENT structure for the root itself
144                   is numbered 0.
145
146       fts_errno   If fts_children() or fts_read() returns an FTSENT structure
147                   whose fts_info field is set to FTS_DNR, FTS_ERR, or FTS_NS,
148                   the fts_errno field contains the error  number  (i.e.,  the
149                   errno value) specifying the cause of the error.  Otherwise,
150                   the contents of the fts_errno field are undefined.
151
152       fts_number  This field is provided for the use of the application  pro‐
153                   gram  and is not modified by the fts functions.  It is ini‐
154                   tialized to 0.
155
156       fts_pointer This field is provided for the use of the application  pro‐
157                   gram  and is not modified by the fts functions.  It is ini‐
158                   tialized to NULL.
159
160       fts_parent  A pointer to the FTSENT structure referencing the  file  in
161                   the  hierarchy immediately above the current file, that is,
162                   the directory of which this file is  a  member.   A  parent
163                   structure  for the initial entry point is provided as well,
164                   however, only the fts_level,  fts_number,  and  fts_pointer
165                   fields are guaranteed to be initialized.
166
167       fts_link    Upon  return from the fts_children() function, the fts_link
168                   field points to the next structure in  the  NULL-terminated
169                   linked  list of directory members.  Otherwise, the contents
170                   of the fts_link field are undefined.
171
172       fts_cycle   If a  directory  causes  a  cycle  in  the  hierarchy  (see
173                   FTS_DC), either because of a hard link between two directo‐
174                   ries, or a symbolic  link  pointing  to  a  directory,  the
175                   fts_cycle  field  of the structure will point to the FTSENT
176                   structure in the hierarchy that references the same file as
177                   the  current  FTSENT structure.  Otherwise, the contents of
178                   the fts_cycle field are undefined.
179
180       fts_statp   A pointer to stat(2) information for the file.
181
182       A single buffer is used for all of the paths of all of the files in the
183       file  hierarchy.   Therefore,  the  fts_path and fts_accpath fields are
184       guaranteed to be  null-terminated  only  for  the  file  most  recently
185       returned  by  fts_read().   To  use these fields to reference any files
186       represented by other FTSENT structures will require that the path  buf‐
187       fer  be  modified using the information contained in that FTSENT struc‐
188       ture's fts_pathlen field.  Any  such  modifications  should  be  undone
189       before  further  calls to fts_read() are attempted.  The fts_name field
190       is always null-terminated.
191
192   fts_open()
193       The fts_open() function takes a pointer to an array of character point‐
194       ers  naming one or more paths which make up a logical file hierarchy to
195       be traversed.  The array must be terminated by a null pointer.
196
197       There are a number of options, at least one of which (either  FTS_LOGI‐
198       CAL  or  FTS_PHYSICAL)  must be specified.  The options are selected by
199       ORing the following values:
200
201       FTS_COMFOLLOW This option causes any symbolic link specified as a  root
202                     path  to be followed immediately whether or not FTS_LOGI‐
203                     CAL is also specified.
204
205       FTS_LOGICAL   This option causes the  fts  routines  to  return  FTSENT
206                     structures  for  the targets of symbolic links instead of
207                     the symbolic links themselves.  If this  option  is  set,
208                     the  only  symbolic links for which FTSENT structures are
209                     returned to the application are those referencing  nonex‐
210                     istent files.  Either FTS_LOGICAL or FTS_PHYSICAL must be
211                     provided to the fts_open() function.
212
213       FTS_NOCHDIR   As a performance optimization, the fts  functions  change
214                     directories  as  they  walk the file hierarchy.  This has
215                     the side-effect that an application cannot rely on  being
216                     in  any  particular  directory during the traversal.  The
217                     FTS_NOCHDIR option turns off this optimization,  and  the
218                     fts  functions  will  not  change  the current directory.
219                     Note that applications should not themselves change their
220                     current   directory   and  try  to  access  files  unless
221                     FTS_NOCHDIR is specified and absolute pathnames were pro‐
222                     vided as arguments to fts_open().
223
224       FTS_NOSTAT    By  default,  returned  FTSENT  structures reference file
225                     characteristic information (the  statp  field)  for  each
226                     file  visited.  This option relaxes that requirement as a
227                     performance optimization, allowing the fts  functions  to
228                     set the fts_info field to FTS_NSOK and leave the contents
229                     of the statp field undefined.
230
231       FTS_PHYSICAL  This option causes the  fts  routines  to  return  FTSENT
232                     structures  for  symbolic links themselves instead of the
233                     target files they point  to.   If  this  option  is  set,
234                     FTSENT structures for all symbolic links in the hierarchy
235                     are returned to the application.  Either  FTS_LOGICAL  or
236                     FTS_PHYSICAL must be provided to the fts_open() function.
237
238       FTS_SEEDOT    By  default,  unless they are specified as path arguments
239                     to fts_open(), any files named "."  or ".."   encountered
240                     in  the  file  hierarchy are ignored.  This option causes
241                     the fts routines to return FTSENT structures for them.
242
243       FTS_XDEV      This option prevents fts from descending into directories
244                     that  have  a  different device number than the file from
245                     which the descent began.
246
247       The argument compar() specifies a user-defined function  which  may  be
248       used to order the traversal of the hierarchy.  It takes two pointers to
249       pointers to FTSENT structures as arguments and should return a negative
250       value,  zero, or a positive value to indicate if the file referenced by
251       its first argument comes before, in  any  order  with  respect  to,  or
252       after,  the  file  referenced by its second argument.  The fts_accpath,
253       fts_path, and fts_pathlen fields of the FTSENT structures may never  be
254       used  in  this  comparison.   If the fts_info field is set to FTS_NS or
255       FTS_NSOK, the fts_statp field may not either.  If the compar() argument
256       is  NULL,  the  directory  traversal  order  is  in the order listed in
257       path_argv for the root paths, and in the order listed in the  directory
258       for everything else.
259
260   fts_read()
261       The  fts_read()  function  returns  a  pointer  to  an FTSENT structure
262       describing a file in the hierarchy.  Directories (that are readable and
263       do  not  cause cycles) are visited at least twice, once in preorder and
264       once in postorder.  All other files are visited at least  once.   (Hard
265       links between directories that do not cause cycles or symbolic links to
266       symbolic links may cause files to be visited more than once, or  direc‐
267       tories more than twice.)
268
269       If  all  the  members  of  the hierarchy have been returned, fts_read()
270       returns NULL and sets the external variable errno to 0.   If  an  error
271       unrelated  to  a  file in the hierarchy occurs, fts_read() returns NULL
272       and sets errno appropriately.  If an error related to a  returned  file
273       occurs,  a pointer to an FTSENT structure is returned, and errno may or
274       may not have been set (see fts_info).
275
276       The FTSENT structures returned by fts_read() may be overwritten after a
277       call to fts_close() on the same file hierarchy stream, or, after a call
278       to fts_read() on the same file hierarchy stream unless they represent a
279       file  of  type  directory,  in  which case they will not be overwritten
280       until after a call to fts_read() after the FTSENT  structure  has  been
281       returned by the function fts_read() in postorder.
282
283   fts_children()
284       The  fts_children()  function  returns a pointer to an FTSENT structure
285       describing the first entry in a  NULL-terminated  linked  list  of  the
286       files  in  the  directory  represented  by  the  FTSENT  structure most
287       recently returned by  fts_read().   The  list  is  linked  through  the
288       fts_link  field  of  the  FTSENT structure, and is ordered by the user-
289       specified comparison function, if any.   Repeated  calls  to  fts_chil‐
290       dren() will re-create this linked list.
291
292       As  a special case, if fts_read() has not yet been called for a hierar‐
293       chy, fts_children() will return a pointer to the files in  the  logical
294       directory  specified to fts_open(), that is, the arguments specified to
295       fts_open().  Otherwise, if the FTSENT structure most recently  returned
296       by  fts_read()  is  not  a  directory being visited in preorder, or the
297       directory does not contain any files, fts_children() returns  NULL  and
298       sets  errno  to  zero.  If an error occurs, fts_children() returns NULL
299       and sets errno appropriately.
300
301       The FTSENT structures returned by  fts_children()  may  be  overwritten
302       after  a call to fts_children(), fts_close(), or fts_read() on the same
303       file hierarchy stream.
304
305       The instr argument is either zero or the following value:
306
307       FTS_NAMEONLY Only the names of the files are needed.  The  contents  of
308                    all  the  fields in the returned linked list of structures
309                    are undefined with  the  exception  of  the  fts_name  and
310                    fts_namelen fields.
311
312   fts_set()
313       The function fts_set() allows the user application to determine further
314       processing for the file f of the stream ftsp.  The  fts_set()  function
315       returns 0 on success, and -1 if an error occurs.
316
317       The  instr  argument  is  either 0 (meaning "do nothing") or one of the
318       following values:
319
320       FTS_AGAIN    Revisit the file; any file type  may  be  revisited.   The
321                    next  call  to fts_read() will return the referenced file.
322                    The fts_stat and fts_info fields of the structure will  be
323                    reinitialized  at that time, but no other fields will have
324                    been changed.  This option is meaningful only for the most
325                    recently returned file from fts_read().  Normal use is for
326                    postorder directory visits, where it causes the  directory
327                    to  be  revisited (in both preorder and postorder) as well
328                    as all of its descendants.
329
330       FTS_FOLLOW   The referenced file must be a symbolic link.  If the  ref‐
331                    erenced   file  is  the  one  most  recently  returned  by
332                    fts_read(), the next call to fts_read() returns  the  file
333                    with  the  fts_info  and fts_statp fields reinitialized to
334                    reflect the target of the symbolic  link  instead  of  the
335                    symbolic  link  itself.   If the file is one of those most
336                    recently returned  by  fts_children(),  the  fts_info  and
337                    fts_statp  fields  of  the  structure,  when  returned  by
338                    fts_read(), will reflect the target of the  symbolic  link
339                    instead  of  the symbolic link itself.  In either case, if
340                    the target of the symbolic link does not exist, the fields
341                    of  the  returned  structure  will  be  unchanged  and the
342                    fts_info field will be set to FTS_SLNONE.
343
344                    If the target of the link is  a  directory,  the  preorder
345                    return,  followed by the return of all of its descendants,
346                    followed by a postorder return, is done.
347
348       FTS_SKIP     No descendants of this file are visited.  The file may  be
349                    one  of  those  most recently returned by either fts_chil‐
350                    dren() or fts_read().
351
352   fts_close()
353       The fts_close() function closes the file hierarchy stream  referred  to
354       by  ftsp and restores the current directory to the directory from which
355       fts_open() was called to open ftsp.  The fts_close() function returns 0
356       on success, and -1 if an error occurs.
357

ERRORS

359       The  function  fts_open()  may fail and set errno for any of the errors
360       specified for open(2) and malloc(3).
361
362       The function fts_close() may fail and set errno for any of  the  errors
363       specified for chdir(2) and close(2).
364
365       The  functions fts_read() and fts_children() may fail and set errno for
366       any of the errors specified for chdir(2), malloc(3), opendir(3),  read‐
367       dir(3), and stat(2).
368
369       In addition, fts_children(), fts_open(), and fts_set() may fail and set
370       errno as follows:
371
372       EINVAL options or instr was invalid.
373

VERSIONS

375       These functions are available in Linux since glibc2.
376

ATTRIBUTES

378       For  an  explanation  of  the  terms  used   in   this   section,   see
379       attributes(7).
380
381       ┌───────────────────────────────────┬───────────────┬───────────┐
382Interface                          Attribute     Value     
383       ├───────────────────────────────────┼───────────────┼───────────┤
384fts_open(), fts_set(), fts_close() │ Thread safety │ MT-Safe   │
385       ├───────────────────────────────────┼───────────────┼───────────┤
386fts_read(), fts_children()         │ Thread safety │ MT-Unsafe │
387       └───────────────────────────────────┴───────────────┴───────────┘
388

CONFORMING TO

390       4.4BSD.
391

BUGS

393       In versions of glibc before 2.23, all of the APIs described in this man
394       page are not safe when compiling a program using the  LFS  APIs  (e.g.,
395       when compiling with -D_FILE_OFFSET_BITS=64).
396

SEE ALSO

398       find(1), chdir(2), stat(2), ftw(3), qsort(3)
399

COLOPHON

401       This  page  is  part of release 5.04 of the Linux man-pages project.  A
402       description of the project, information about reporting bugs,  and  the
403       latest     version     of     this    page,    can    be    found    at
404       https://www.kernel.org/doc/man-pages/.
405
406
407
408Linux                             2018-02-02                            FTS(3)
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