1FTW(3)                     Linux Programmer's Manual                    FTW(3)
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3
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NAME

6       ftw, nftw - file tree walk
7

SYNOPSIS

9       #include <ftw.h>
10
11       int nftw(const char *dirpath,
12               int (*fn) (const char *fpath, const struct stat *sb,
13                          int typeflag, struct FTW *ftwbuf),
14               int nopenfd, int flags);
15
16       #include <ftw.h>
17
18       int ftw(const char *dirpath,
19               int (*fn) (const char *fpath, const struct stat *sb,
20                          int typeflag),
21               int nopenfd);
22
23   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24
25       nftw(): _XOPEN_SOURCE >= 500
26

DESCRIPTION

28       nftw()  walks  through  the  directory  tree  that is located under the
29       directory dirpath, and calls fn() once for each entry in the tree.   By
30       default,  directories  are  handled before the files and subdirectories
31       they contain (preorder traversal).
32
33       To avoid using up  all  of  the  calling  process's  file  descriptors,
34       nopenfd  specifies  the  maximum number of directories that nftw() will
35       hold open simultaneously.  When the search depth exceeds  this,  nftw()
36       will  become slower because directories have to be closed and reopened.
37       nftw() uses at most one file descriptor for each level in the directory
38       tree.
39
40       For  each  entry  found  in the tree, nftw() calls fn() with four argu‐
41       ments: fpath, sb, typeflag, and ftwbuf.  fpath is the pathname  of  the
42       entry,  and  is  expressed either as a pathname relative to the calling
43       process's current working directory at the time of the call to  nftw(),
44       if  dirpath  was  expressed  as  a relative pathname, or as an absolute
45       pathname, if dirpath was expressed as an absolute pathname.   sb  is  a
46       pointer to the stat structure returned by a call to stat(2) for fpath.
47
48       The  typeflag argument passed to fn() is an integer that has one of the
49       following values:
50
51       FTW_F  fpath is a regular file.
52
53       FTW_D  fpath is a directory.
54
55       FTW_DNR
56              fpath is a directory which can't be read.
57
58       FTW_DP fpath is a directory, and FTW_DEPTH was specified in flags.  (If
59              FTW_DEPTH  was  not  specified  in  flags, then directories will
60              always be visited with typeflag set to FTW_D.)  All of the files
61              and subdirectories within fpath have been processed.
62
63       FTW_NS The  stat(2) call failed on fpath, which is not a symbolic link.
64              The probable cause for this is that the caller had read  permis‐
65              sion  on  the parent directory, so that the filename fpath could
66              be seen, but did not have execute permission, so that  the  file
67              could  not  be  reached for stat(2).  The contents of the buffer
68              pointed to by sb are undefined.
69
70       FTW_SL fpath is a symbolic link, and FTW_PHYS was set in flags.
71
72       FTW_SLN
73              fpath is a symbolic link pointing to a nonexistent file.   (This
74              occurs  only  if FTW_PHYS is not set.)  On most implementations,
75              in this case the sb argument passed to fn() contains information
76              returned  by  performing lstat(2) on the symbolic link.  For the
77              details on Linux, see BUGS.
78
79       The fourth argument (ftwbuf) that nftw() supplies when calling fn()  is
80       a pointer to a structure of type FTW:
81
82           struct FTW {
83               int base;
84               int level;
85           };
86
87       base  is  the  offset of the filename (i.e., basename component) in the
88       pathname given in fpath.  level is the depth of fpath in the  directory
89       tree, relative to the root of the tree (dirpath, which has depth 0).
90
91       To  stop  the  tree walk, fn() returns a nonzero value; this value will
92       become the return value of nftw().  As long as fn() returns  0,  nftw()
93       will  continue  either until it has traversed the entire tree, in which
94       case it will return zero, or until it encounters an error  (such  as  a
95       malloc(3) failure), in which case it will return -1.
96
97       Because  nftw() uses dynamic data structures, the only safe way to exit
98       out of a tree walk is to return a nonzero value from fn().  To allow  a
99       signal  to  terminate  the walk without causing a memory leak, have the
100       handler set  a  global  flag  that  is  checked  by  fn().   Don't  use
101       longjmp(3) unless the program is going to terminate.
102
103       The  flags  argument  of  nftw() is formed by ORing zero or more of the
104       following flags:
105
106       FTW_ACTIONRETVAL (since glibc 2.3.3)
107              If this glibc-specific flag is  set,  then  nftw()  handles  the
108              return  value  from fn() differently.  fn() should return one of
109              the following values:
110
111              FTW_CONTINUE
112                     Instructs nftw() to continue normally.
113
114              FTW_SKIP_SIBLINGS
115                     If fn() returns this value, then siblings of the  current
116                     entry  will  be  skipped, and processing continues in the
117                     parent.
118
119              FTW_SKIP_SUBTREE
120                     If fn() is called with  an  entry  that  is  a  directory
121                     (typeflag  is  FTW_D),  this  return  value  will prevent
122                     objects within that directory from being passed as  argu‐
123                     ments to fn().  nftw() continues processing with the next
124                     sibling of the directory.
125
126              FTW_STOP
127                     Causes nftw() to return immediately with the return value
128                     FTW_STOP.
129
130              Other  return values could be associated with new actions in the
131              future; fn() should not return values other  than  those  listed
132              above.
133
134              The  feature  test  macro  _GNU_SOURCE  must  be defined (before
135              including any header files) in order to obtain the definition of
136              FTW_ACTIONRETVAL from <ftw.h>.
137
138       FTW_CHDIR
139              If set, do a chdir(2) to each directory before handling its con‐
140              tents.  This is useful if the  program  needs  to  perform  some
141              action  in  the  directory  in which fpath resides.  (Specifying
142              this flag has no effect on the pathname that is  passed  in  the
143              fpath argument of fn.)
144
145       FTW_DEPTH
146              If  set,  do  a post-order traversal, that is, call fn() for the
147              directory itself after handling the contents  of  the  directory
148              and  its subdirectories.  (By default, each directory is handled
149              before its contents.)
150
151       FTW_MOUNT
152              If set, stay within the same  filesystem  (i.e.,  do  not  cross
153              mount points).
154
155       FTW_PHYS
156              If  set, do not follow symbolic links.  (This is what you want.)
157              If not set, symbolic links are followed, but no file is reported
158              twice.
159
160              If  FTW_PHYS is not set, but FTW_DEPTH is set, then the function
161              fn() is never called for a directory that would be a  descendant
162              of itself.
163
164   ftw()
165       ftw() is an older function that offers a subset of the functionality of
166       nftw().  The notable differences are as follows:
167
168       *  ftw() has no flags argument.  It behaves the same as when nftw()  is
169          called with flags specified as zero.
170
171       *  The callback function, fn(), is not supplied with a fourth argument.
172
173       *  The  range  of  values that is passed via the typeflag argument sup‐
174          plied to fn() is smaller: just FTW_F, FTW_D,  FTW_DNR,  FTW_NS,  and
175          (possibly) FTW_SL.
176

RETURN VALUE

178       These functions return 0 on success, and -1 if an error occurs.
179
180       If fn() returns nonzero, then the tree walk is terminated and the value
181       returned by fn() is returned as the result of ftw() or nftw().
182
183       If nftw() is called with  the  FTW_ACTIONRETVAL  flag,  then  the  only
184       nonzero value that should be used by fn() to terminate the tree walk is
185       FTW_STOP, and that value is returned as the result of nftw().
186

VERSIONS

188       nftw() is available under glibc since version 2.1.
189

ATTRIBUTES

191       For  an  explanation  of  the  terms  used   in   this   section,   see
192       attributes(7).
193
194       ┌──────────┬───────────────┬─────────────┐
195Interface Attribute     Value       
196       ├──────────┼───────────────┼─────────────┤
197nftw()    │ Thread safety │ MT-Safe cwd │
198       ├──────────┼───────────────┼─────────────┤
199ftw()     │ Thread safety │ MT-Safe     │
200       └──────────┴───────────────┴─────────────┘
201

CONFORMING TO

203       POSIX.1-2001,  POSIX.1-2008,  SVr4, SUSv1.  POSIX.1-2008 marks ftw() as
204       obsolete.
205

NOTES

207       POSIX.1-2008 notes that the results are unspecified if fn does not pre‐
208       serve the current working directory.
209
210       The function nftw() and the use of FTW_SL with ftw() were introduced in
211       SUSv1.
212
213       In some implementations (e.g., glibc), ftw() will never use FTW_SL,  on
214       other  systems  FTW_SL occurs only for symbolic links that do not point
215       to an existing file, and again on other systems ftw() will  use  FTW_SL
216       for  each  symbolic  link.   If  fpath  is  a symbolic link and stat(2)
217       failed, POSIX.1-2008 states that it  is  undefined  whether  FTW_NS  or
218       FTW_SL is passed in typeflag.  For predictable results, use nftw().
219

BUGS

221       In  the  specification  of  nftw(),  POSIX.1  notes that when FTW_NS is
222       passed as the typeflag argument of fn(), then the contents of the  buf‐
223       fer pointed to by the sb argument are undefined.  The standard makes no
224       such statement for the case where FTW_SLN is passed in  typeflag,  with
225       the  implication  that  the contents of the buffer pointed to by sb are
226       defined.  And indeed this is the case on most implementations: the buf‐
227       fer pointed to by sb contains the results produced by applying lstat(2)
228       to the symbolic link.  In early glibc, the behavior was the same.  How‐
229       ever,  since glibc 2.4, the contents of the buffer pointed to by sb are
230       undefined when FTW_SLN is passed in typeflag.  This change  appears  to
231       be  an unintended regression, but it is not (yet) clear if the behavior
232       will be restored to that provided in the original glibc  implementation
233       (and on other implementations).
234

EXAMPLE

236       The following program traverses the directory tree under the path named
237       in its first command-line argument, or under the current  directory  if
238       no  argument  is  supplied.  It displays various information about each
239       file.  The second command-line argument can be used to specify  charac‐
240       ters that control the value assigned to the flags argument when calling
241       nftw().
242
243   Program source
244
245       #define _XOPEN_SOURCE 500
246       #include <ftw.h>
247       #include <stdio.h>
248       #include <stdlib.h>
249       #include <string.h>
250       #include <stdint.h>
251
252       static int
253       display_info(const char *fpath, const struct stat *sb,
254                    int tflag, struct FTW *ftwbuf)
255       {
256           printf("%-3s %2d ",
257                   (tflag == FTW_D) ?   "d"   : (tflag == FTW_DNR) ? "dnr" :
258                   (tflag == FTW_DP) ?  "dp"  : (tflag == FTW_F) ?   "f" :
259                   (tflag == FTW_NS) ?  "ns"  : (tflag == FTW_SL) ?  "sl" :
260                   (tflag == FTW_SLN) ? "sln" : "???",
261                   ftwbuf->level);
262
263           if (tflag == FTW_NS)
264               printf("-------");
265           else
266               printf("%7jd", (intmax_t) sb->st_size);
267
268           printf("   %-40s %d %s\n",
269                   fpath, ftwbuf->base, fpath + ftwbuf->base);
270
271           return 0;           /* To tell nftw() to continue */
272       }
273
274       int
275       main(int argc, char *argv[])
276       {
277           int flags = 0;
278
279           if (argc > 2 && strchr(argv[2], 'd') != NULL)
280               flags |= FTW_DEPTH;
281           if (argc > 2 && strchr(argv[2], 'p') != NULL)
282               flags |= FTW_PHYS;
283
284           if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags)
285                   == -1) {
286               perror("nftw");
287               exit(EXIT_FAILURE);
288           }
289
290           exit(EXIT_SUCCESS);
291       }
292

SEE ALSO

294       stat(2), fts(3), readdir(3)
295

COLOPHON

297       This page is part of release 4.16 of the Linux  man-pages  project.   A
298       description  of  the project, information about reporting bugs, and the
299       latest    version    of    this    page,    can     be     found     at
300       https://www.kernel.org/doc/man-pages/.
301
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303
304Linux                             2017-09-15                            FTW(3)
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