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 #include <ftw.h>
17 int ftw(const char *dirpath,
19 int (*fn) (const char *fpath, const struct stat *sb,
20 int typeflag),
21 int nopenfd);
22 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24 nftw(): _XOPEN_SOURCE >= 500
26
28 nftw() walks through the directory tree that is located under the di‐
29 rectory 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 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 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 The typeflag argument passed to fn() is an integer that has one of the
49 following values:
50 FTW_F fpath is a regular file.
52 FTW_D fpath is a directory.
54 FTW_DNR
56 fpath is a directory which can't be read.
57 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 al‐
60 ways be visited with typeflag set to FTW_D.) All of the files
61 and subdirectories within fpath have been processed.
62 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 FTW_SL fpath is a symbolic link, and FTW_PHYS was set in flags.
71 FTW_SLN
73 fpath is a symbolic link pointing to a nonexistent file. (This
74 occurs only if FTW_PHYS is not set.) In this case the sb argu‐
75 ment passed to fn() contains information returned by performing
76 lstat(2) on the "dangling" symbolic link. (But see BUGS.)
77 The fourth argument (ftwbuf) that nftw() supplies when calling fn() is
79 a pointer to a structure of type FTW:
80 struct FTW {
82 int base;
83 int level;
84 };
85 base is the offset of the filename (i.e., basename component) in the
87 pathname given in fpath. level is the depth of fpath in the directory
88 tree, relative to the root of the tree (dirpath, which has depth 0).
89 To stop the tree walk, fn() returns a nonzero value; this value will
91 become the return value of nftw(). As long as fn() returns 0, nftw()
92 will continue either until it has traversed the entire tree, in which
93 case it will return zero, or until it encounters an error (such as a
94 malloc(3) failure), in which case it will return -1.
95 Because nftw() uses dynamic data structures, the only safe way to exit
97 out of a tree walk is to return a nonzero value from fn(). To allow a
98 signal to terminate the walk without causing a memory leak, have the
99 handler set a global flag that is checked by fn(). Don't use
100 longjmp(3) unless the program is going to terminate.
101 The flags argument of nftw() is formed by ORing zero or more of the
103 following flags:
104 FTW_ACTIONRETVAL (since glibc 2.3.3)
106 If this glibc-specific flag is set, then nftw() handles the re‐
107 turn value from fn() differently. fn() should return one of the
108 following values:
109 FTW_CONTINUE
111 Instructs nftw() to continue normally.
112 FTW_SKIP_SIBLINGS
114 If fn() returns this value, then siblings of the current
115 entry will be skipped, and processing continues in the
116 parent.
117 FTW_SKIP_SUBTREE
119 If fn() is called with an entry that is a directory
120 (typeflag is FTW_D), this return value will prevent ob‐
121 jects within that directory from being passed as argu‐
122 ments to fn(). nftw() continues processing with the next
123 sibling of the directory.
124 FTW_STOP
126 Causes nftw() to return immediately with the return value
127 FTW_STOP.
128 Other return values could be associated with new actions in the
130 future; fn() should not return values other than those listed
131 above.
132 The feature test macro _GNU_SOURCE must be defined (before in‐
134 cluding any header files) in order to obtain the definition of
135 FTW_ACTIONRETVAL from <ftw.h>.
136 FTW_CHDIR
138 If set, do a chdir(2) to each directory before handling its con‐
139 tents. This is useful if the program needs to perform some ac‐
140 tion in the directory in which fpath resides. (Specifying this
141 flag has no effect on the pathname that is passed in the fpath
142 argument of fn.)
143 FTW_DEPTH
145 If set, do a post-order traversal, that is, call fn() for the
146 directory itself after handling the contents of the directory
147 and its subdirectories. (By default, each directory is handled
148 before its contents.)
149 FTW_MOUNT
151 If set, stay within the same filesystem (i.e., do not cross
152 mount points).
153 FTW_PHYS
155 If set, do not follow symbolic links. (This is what you want.)
156 If not set, symbolic links are followed, but no file is reported
157 twice.
158 If FTW_PHYS is not set, but FTW_DEPTH is set, then the function
160 fn() is never called for a directory that would be a descendant
161 of itself.
162 ftw()
164 ftw() is an older function that offers a subset of the functionality of
165 nftw(). The notable differences are as follows:
166 * ftw() has no flags argument. It behaves the same as when nftw() is
168 called with flags specified as zero.
169 * The callback function, fn(), is not supplied with a fourth argument.
171 * The range of values that is passed via the typeflag argument sup‐
173 plied to fn() is smaller: just FTW_F, FTW_D, FTW_DNR, FTW_NS, and
174 (possibly) FTW_SL.
175
177 These functions return 0 on success, and -1 if an error occurs.
178 If fn() returns nonzero, then the tree walk is terminated and the value
180 returned by fn() is returned as the result of ftw() or nftw().
181 If nftw() is called with the FTW_ACTIONRETVAL flag, then the only non‐
183 zero value that should be used by fn() to terminate the tree walk is
184 FTW_STOP, and that value is returned as the result of nftw().
185
187 nftw() is available under glibc since version 2.1.
188
190 For an explanation of the terms used in this section, see at‐
191 tributes(7).
192 ┌──────────┬───────────────┬─────────────┐
194 │Interface │ Attribute │ Value │
195 ├──────────┼───────────────┼─────────────┤
196 │nftw() │ Thread safety │ MT-Safe cwd │
197 ├──────────┼───────────────┼─────────────┤
198 │ftw() │ Thread safety │ MT-Safe │
199 └──────────┴───────────────┴─────────────┘
200
202 POSIX.1-2001, POSIX.1-2008, SVr4, SUSv1. POSIX.1-2008 marks ftw() as
203 obsolete.
204
206 POSIX.1-2008 notes that the results are unspecified if fn does not pre‐
207 serve the current working directory.
208 The function nftw() and the use of FTW_SL with ftw() were introduced in
210 SUSv1.
211 In some implementations (e.g., glibc), ftw() will never use FTW_SL, on
213 other systems FTW_SL occurs only for symbolic links that do not point
214 to an existing file, and again on other systems ftw() will use FTW_SL
215 for each symbolic link. If fpath is a symbolic link and stat(2)
216 failed, POSIX.1-2008 states that it is undefined whether FTW_NS or
217 FTW_SL is passed in typeflag. For predictable results, use nftw().
218
220 According to POSIX.1-2008, when the typeflag argument passed to fn()
221 contains FTW_SLN, the buffer pointed to by sb should contain informa‐
222 tion about the dangling symbolic link (obtained by calling lstat(2) on
223 the link). Early glibc versions correctly followed the POSIX specifi‐
224 cation on this point. However, as a result of a regression introduced
225 in glibc 2.4, the contents of the buffer pointed to by sb were unde‐
226 fined when FTW_SLN is passed in typeflag. (More precisely, the con‐
227 tents of the buffer were left unchanged in this case.) This regression
228 was eventually fixed in glibc 2.30, so that the glibc implementation
229 (once more) follows the POSIX specification.
230
232 The following program traverses the directory tree under the path named
233 in its first command-line argument, or under the current directory if
234 no argument is supplied. It displays various information about each
235 file. The second command-line argument can be used to specify charac‐
236 ters that control the value assigned to the flags argument when calling
237 nftw().
238 Program source
240 #define _XOPEN_SOURCE 500
242 #include <ftw.h>
243 #include <stdio.h>
244 #include <stdlib.h>
245 #include <string.h>
246 #include <stdint.h>
247 static int
249 display_info(const char *fpath, const struct stat *sb,
250 int tflag, struct FTW *ftwbuf)
251 {
252 printf("%-3s %2d ",
253 (tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" :
254 (tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ? "f" :
255 (tflag == FTW_NS) ? "ns" : (tflag == FTW_SL) ? "sl" :
256 (tflag == FTW_SLN) ? "sln" : "???",
257 ftwbuf->level);
258 if (tflag == FTW_NS)
260 printf("-------");
261 else
262 printf("%7jd", (intmax_t) sb->st_size);
263 printf(" %-40s %d %s\n",
265 fpath, ftwbuf->base, fpath + ftwbuf->base);
266 return 0; /* To tell nftw() to continue */
268 }
269 int
271 main(int argc, char *argv[])
272 {
273 int flags = 0;
274 if (argc > 2 && strchr(argv[2], 'd') != NULL)
276 flags |= FTW_DEPTH;
277 if (argc > 2 && strchr(argv[2], 'p') != NULL)
278 flags |= FTW_PHYS;
279 if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags)
281 == -1) {
282 perror("nftw");
283 exit(EXIT_FAILURE);
284 }
285 exit(EXIT_SUCCESS);
287 }
288
290 stat(2), fts(3), readdir(3)
291
293 This page is part of release 5.10 of the Linux man-pages project. A
294 description of the project, information about reporting bugs, and the
295 latest version of this page, can be found at
296 https://www.kernel.org/doc/man-pages/.
297Linux 2020-06-09 FTW(3)