FTW(3) | Linux Programmer's Manual | FTW(3) |
NAME
ftw, nftw - file tree walkSYNOPSIS
#include<ftw.h>
int ftw(const char * dirpath ,
int (* fn ) (const char * fpath , const struct stat * sb ,
int typeflag ),
int nopenfd );
#define _XOPEN_SOURCE 500 /* See feature_test_macros(7) */ #include
<ftw.h>
int nftw(const char * dirpath ,
int (* fn ) (const char * fpath , const struct stat * sb ,
int typeflag , struct FTW * ftwbuf ),
int nopenfd , int flags );
DESCRIPTION
ftw() walks through the directory tree that is located under the directory dirpath, and calls fn() once for each entry in the tree. By default, directories are handled before the files and subdirectories they contain (preorder traversal).- FTW_F
- fpath is a regular file.
- FTW_D
- fpath is a directory.
- FTW_DNR
- fpath is a directory which can't be read.
- FTW_NS
-
The
stat(2) call failed on
fpath, which is not a symbolic link.
To stop the tree walk, fn() returns a nonzero value; this value will become the return value of ftw(). As long as fn() returns 0, ftw() will continue either until it has traversed the entire tree, in which case it will return zero, or until it encounters an error (such as a malloc(3) failure), in which case it will return -1.
Because ftw() uses dynamic data structures, the only safe way to exit out of a tree walk is to return a nonzero value from fn(). To allow a signal to terminate the walk without causing a memory leak, have the handler set a global flag that is checked by fn(). Don't use longjmp(3) unless the program is going to terminate.
nftw()
The function nftw() is the same as ftw(), except that it has one additional argument, flags, and calls fn() with one more argument, ftwbuf.- FTW_ACTIONRETVAL (since glibc 2.3.3)
- If this glibc-specific flag is set, then nftw() handles the return value from fn() differently. fn() should return one of the following values:
- FTW_CONTINUE
- Instructs nftw() to continue normally.
- FTW_SKIP_SIBLINGS
- If fn() returns this value, then siblings of the current entry will be skipped, and processing continues in the parent.
- FTW_SKIP_SUBTREE
- If fn() is called with an entry that is a directory ( typeflag is FTW_D), this return value will prevent objects within that directory from being passed as arguments to fn(). nftw() continues processing with the next sibling of the directory.
- FTW_STOP
- Causes nftw() to return immediately with the return value FTW_STOP.
Other return values could be associated with new actions in the future; fn() should not return values other than those listed above.
The feature test macro _GNU_SOURCE must be defined (before including any header files) in order to obtain the definition of FTW_ACTIONRETVAL from <ftw.h>.
- FTW_CHDIR
- If set, do a chdir(2) to each directory before handling its contents. This is useful if the program needs to perform some action in the directory in which fpath resides.
- FTW_DEPTH
- If set, do a post-order traversal, that is, call fn() for the directory itself after handling the contents of the directory and its subdirectories. (By default, each directory is handled before its contents.)
- FTW_MOUNT
- If set, stay within the same file system (i.e., do not cross mount points).
- FTW_PHYS
-
If set, do not follow symbolic links. (This is what you want.) If not set, symbolic links are followed, but no file is reported twice.
For each entry in the directory tree, nftw() calls fn() with four arguments. fpath and sb are as for ftw(). typeflag may receive any of the same values as with ftw(), or any of the following values:
- FTW_DP
- fpath is a directory, and FTW_DEPTH was specified in flags. All of the files and subdirectories within fpath have been processed.
- FTW_SL
- fpath is a symbolic link, and FTW_PHYS was set in flags.
- FTW_SLN
- fpath is a symbolic link pointing to a nonexistent file. (This occurs only if FTW_PHYS is not set.)
The fourth argument that nftw() supplies when calling fn() is a structure of type FTW:
struct FTW {
int base;
int level;
};
base is the offset of the filename (i.e., basename component) in the pathname given in fpath. level is the depth of fpath in the directory tree, relative to the root of the tree ( dirpath, which has depth 0).
RETURN VALUE
These functions return 0 on success, and -1 if an error occurs.CONFORMING TO
POSIX.1-2001, SVr4, SUSv1. POSIX.1-2008 marks ftw() as obsolete.NOTES
POSIX.1-2001 note that the results are unspecified if fn does not preserve the current working directory.The function nftw() and the use of FTW_SL with ftw() were introduced in SUSv1.
On some systems ftw() will never use FTW_SL, on other systems FTW_SL occurs only for symbolic links that do not point to an existing file, and again on other systems ftw() will use FTW_SL for each symbolic link. For predictable control, use nftw().
Under Linux, libc4 and libc5 and glibc 2.0.6 will use FTW_F for all objects (files, symbolic links, FIFOs, etc.) that can be stat'ed but are not a directory.
The function nftw() is available since glibc 2.1.
FTW_ACTIONRETVAL is glibc-specific.
EXAMPLE
The following program traverses the directory tree under the path named in its first command-line argument, or under the current directory if no argument is supplied. It displays various information about each file. The second command-line argument can be used to specify characters that control the value assigned to the flags argument when calling nftw().
#define _XOPEN_SOURCE 500
#include <ftw.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
static int
display_info(const char *fpath, const struct stat *sb,
int tflag, struct FTW *ftwbuf)
{
printf("%-3s %2d %7jd %-40s %d %s\n",
(tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" :
(tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ? "f" :
(tflag == FTW_NS) ? "ns" : (tflag == FTW_SL) ? "sl" :
(tflag == FTW_SLN) ? "sln" : "???",
ftwbuf->level, (intmax_t) sb->st_size,
fpath, ftwbuf->base, fpath + ftwbuf->base);
return 0; /* To tell nftw() to continue */
}
int
main(int argc, char *argv[])
{
int flags = 0;
if (argc > 2 && strchr(argv[2], 'd') != NULL)
flags |= FTW_DEPTH;
if (argc > 2 && strchr(argv[2], 'p') != NULL)
flags |= FTW_PHYS;
if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags)
== -1) {
perror("nftw");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
SEE ALSO
stat(2), fts(3), readdir(3)COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.2010-09-20 | Linux |