1FTW(3) Linux Programmer's Manual FTW(3)
2
6 ftw, nftw - file tree walk
7
9 #include <ftw.h>
10 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 int ftw(const char *dirpath,
17 int (*fn)(const char *fpath, const struct stat *sb,
18 int typeflag),
19 int nopenfd);
20 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22 nftw():
24 _XOPEN_SOURCE >= 500
25
27 nftw() walks through the directory tree that is located under the di‐
28 rectory dirpath, and calls fn() once for each entry in the tree. By
29 default, directories are handled before the files and subdirectories
30 they contain (preorder traversal).
31 To avoid using up all of the calling process's file descriptors,
33 nopenfd specifies the maximum number of directories that nftw() will
34 hold open simultaneously. When the search depth exceeds this, nftw()
35 will become slower because directories have to be closed and reopened.
36 nftw() uses at most one file descriptor for each level in the directory
37 tree.
38 For each entry found in the tree, nftw() calls fn() with four argu‐
40 ments: fpath, sb, typeflag, and ftwbuf. fpath is the pathname of the
41 entry, and is expressed either as a pathname relative to the calling
42 process's current working directory at the time of the call to nftw(),
43 if dirpath was expressed as a relative pathname, or as an absolute
44 pathname, if dirpath was expressed as an absolute pathname. sb is a
45 pointer to the stat structure returned by a call to stat(2) for fpath.
46 The typeflag argument passed to fn() is an integer that has one of the
48 following values:
49 FTW_F fpath is a regular file.
51 FTW_D fpath is a directory.
53 FTW_DNR
55 fpath is a directory which can't be read.
56 FTW_DP fpath is a directory, and FTW_DEPTH was specified in flags. (If
58 FTW_DEPTH was not specified in flags, then directories will al‐
59 ways be visited with typeflag set to FTW_D.) All of the files
60 and subdirectories within fpath have been processed.
61 FTW_NS The stat(2) call failed on fpath, which is not a symbolic link.
63 The probable cause for this is that the caller had read permis‐
64 sion on the parent directory, so that the filename fpath could
65 be seen, but did not have execute permission, so that the file
66 could not be reached for stat(2). The contents of the buffer
67 pointed to by sb are undefined.
68 FTW_SL fpath is a symbolic link, and FTW_PHYS was set in flags.
70 FTW_SLN
72 fpath is a symbolic link pointing to a nonexistent file. (This
73 occurs only if FTW_PHYS is not set.) In this case the sb argu‐
74 ment passed to fn() contains information returned by performing
75 lstat(2) on the "dangling" symbolic link. (But see BUGS.)
76 The fourth argument (ftwbuf) that nftw() supplies when calling fn() is
78 a pointer to a structure of type FTW:
79 struct FTW {
81 int base;
82 int level;
83 };
84 base is the offset of the filename (i.e., basename component) in the
86 pathname given in fpath. level is the depth of fpath in the directory
87 tree, relative to the root of the tree (dirpath, which has depth 0).
88 To stop the tree walk, fn() returns a nonzero value; this value will
90 become the return value of nftw(). As long as fn() returns 0, nftw()
91 will continue either until it has traversed the entire tree, in which
92 case it will return zero, or until it encounters an error (such as a
93 malloc(3) failure), in which case it will return -1.
94 Because nftw() uses dynamic data structures, the only safe way to exit
96 out of a tree walk is to return a nonzero value from fn(). To allow a
97 signal to terminate the walk without causing a memory leak, have the
98 handler set a global flag that is checked by fn(). Don't use
99 longjmp(3) unless the program is going to terminate.
100 The flags argument of nftw() is formed by ORing zero or more of the
102 following flags:
103 FTW_ACTIONRETVAL (since glibc 2.3.3)
105 If this glibc-specific flag is set, then nftw() handles the re‐
106 turn value from fn() differently. fn() should return one of the
107 following values:
108 FTW_CONTINUE
110 Instructs nftw() to continue normally.
111 FTW_SKIP_SIBLINGS
113 If fn() returns this value, then siblings of the current
114 entry will be skipped, and processing continues in the
115 parent.
116 FTW_SKIP_SUBTREE
118 If fn() is called with an entry that is a directory
119 (typeflag is FTW_D), this return value will prevent ob‐
120 jects within that directory from being passed as argu‐
121 ments to fn(). nftw() continues processing with the next
122 sibling of the directory.
123 FTW_STOP
125 Causes nftw() to return immediately with the return value
126 FTW_STOP.
127 Other return values could be associated with new actions in the
129 future; fn() should not return values other than those listed
130 above.
131 The feature test macro _GNU_SOURCE must be defined (before in‐
133 cluding any header files) in order to obtain the definition of
134 FTW_ACTIONRETVAL from <ftw.h>.
135 FTW_CHDIR
137 If set, do a chdir(2) to each directory before handling its con‐
138 tents. This is useful if the program needs to perform some ac‐
139 tion in the directory in which fpath resides. (Specifying this
140 flag has no effect on the pathname that is passed in the fpath
141 argument of fn.)
142 FTW_DEPTH
144 If set, do a post-order traversal, that is, call fn() for the
145 directory itself after handling the contents of the directory
146 and its subdirectories. (By default, each directory is handled
147 before its contents.)
148 FTW_MOUNT
150 If set, stay within the same filesystem (i.e., do not cross
151 mount points).
152 FTW_PHYS
154 If set, do not follow symbolic links. (This is what you want.)
155 If not set, symbolic links are followed, but no file is reported
156 twice.
157 If FTW_PHYS is not set, but FTW_DEPTH is set, then the function
159 fn() is never called for a directory that would be a descendant
160 of itself.
161 ftw()
163 ftw() is an older function that offers a subset of the functionality of
164 nftw(). The notable differences are as follows:
165 * ftw() has no flags argument. It behaves the same as when nftw() is
167 called with flags specified as zero.
168 * The callback function, fn(), is not supplied with a fourth argument.
170 * The range of values that is passed via the typeflag argument sup‐
172 plied to fn() is smaller: just FTW_F, FTW_D, FTW_DNR, FTW_NS, and
173 (possibly) FTW_SL.
174
176 These functions return 0 on success, and -1 if an error occurs.
177 If fn() returns nonzero, then the tree walk is terminated and the value
179 returned by fn() is returned as the result of ftw() or nftw().
180 If nftw() is called with the FTW_ACTIONRETVAL flag, then the only non‐
182 zero value that should be used by fn() to terminate the tree walk is
183 FTW_STOP, and that value is returned as the result of nftw().
184
186 nftw() is available under glibc since version 2.1.
187
189 For an explanation of the terms used in this section, see at‐
190 tributes(7).
191 ┌────────────────────────────────────────┬───────────────┬─────────────┐
193 │Interface │ Attribute │ Value │
194 ├────────────────────────────────────────┼───────────────┼─────────────┤
195 │nftw() │ Thread safety │ MT-Safe cwd │
196 ├────────────────────────────────────────┼───────────────┼─────────────┤
197 │ftw() │ Thread safety │ MT-Safe │
198 └────────────────────────────────────────┴───────────────┴─────────────┘
199
201 POSIX.1-2001, POSIX.1-2008, SVr4, SUSv1. POSIX.1-2008 marks ftw() as
202 obsolete.
203
205 POSIX.1-2008 notes that the results are unspecified if fn does not pre‐
206 serve the current working directory.
207 The function nftw() and the use of FTW_SL with ftw() were introduced in
209 SUSv1.
210 In some implementations (e.g., glibc), ftw() will never use FTW_SL, on
212 other systems FTW_SL occurs only for symbolic links that do not point
213 to an existing file, and again on other systems ftw() will use FTW_SL
214 for each symbolic link. If fpath is a symbolic link and stat(2)
215 failed, POSIX.1-2008 states that it is undefined whether FTW_NS or
216 FTW_SL is passed in typeflag. For predictable results, use nftw().
217
219 According to POSIX.1-2008, when the typeflag argument passed to fn()
220 contains FTW_SLN, the buffer pointed to by sb should contain informa‐
221 tion about the dangling symbolic link (obtained by calling lstat(2) on
222 the link). Early glibc versions correctly followed the POSIX specifi‐
223 cation on this point. However, as a result of a regression introduced
224 in glibc 2.4, the contents of the buffer pointed to by sb were unde‐
225 fined when FTW_SLN is passed in typeflag. (More precisely, the con‐
226 tents of the buffer were left unchanged in this case.) This regression
227 was eventually fixed in glibc 2.30, so that the glibc implementation
228 (once more) follows the POSIX specification.
229
231 The following program traverses the directory tree under the path named
232 in its first command-line argument, or under the current directory if
233 no argument is supplied. It displays various information about each
234 file. The second command-line argument can be used to specify charac‐
235 ters that control the value assigned to the flags argument when calling
236 nftw().
237 Program source
239 #define _XOPEN_SOURCE 500
241 #include <ftw.h>
242 #include <stdio.h>
243 #include <stdlib.h>
244 #include <string.h>
245 #include <stdint.h>
246 static int
248 display_info(const char *fpath, const struct stat *sb,
249 int tflag, struct FTW *ftwbuf)
250 {
251 printf("%-3s %2d ",
252 (tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" :
253 (tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ? "f" :
254 (tflag == FTW_NS) ? "ns" : (tflag == FTW_SL) ? "sl" :
255 (tflag == FTW_SLN) ? "sln" : "???",
256 ftwbuf->level);
257 if (tflag == FTW_NS)
259 printf("-------");
260 else
261 printf("%7jd", (intmax_t) sb->st_size);
262 printf(" %-40s %d %s\n",
264 fpath, ftwbuf->base, fpath + ftwbuf->base);
265 return 0; /* To tell nftw() to continue */
267 }
268 int
270 main(int argc, char *argv[])
271 {
272 int flags = 0;
273 if (argc > 2 && strchr(argv[2], 'd') != NULL)
275 flags |= FTW_DEPTH;
276 if (argc > 2 && strchr(argv[2], 'p') != NULL)
277 flags |= FTW_PHYS;
278 if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags)
280 == -1) {
281 perror("nftw");
282 exit(EXIT_FAILURE);
283 }
284 exit(EXIT_SUCCESS);
286 }
287
289 stat(2), fts(3), readdir(3)
290
292 This page is part of release 5.12 of the Linux man-pages project. A
293 description of the project, information about reporting bugs, and the
294 latest version of this page, can be found at
295 https://www.kernel.org/doc/man-pages/.
296Linux 2021-03-22 FTW(3)