ftw

Sommaire

NAME

ftw, nftw - file tree walk

SYNOPSIS

 #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
 #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 (pre-order traversal).

To avoid using up all of the calling process's file descriptors, nopenfd specifies the maximum number of directories that ftw() will hold open simultaneously. When the search depth exceeds this, ftw() will become slower because directories have to be closed and reopened. ftw() uses at most one file descriptor for each level in the directory tree.

For each entry found in the tree, ftw() calls fn() with three arguments: fpath, sb, and typeflag. fpath is the pathname of the entry relative to dirpath. sb is a pointer to the stat structure returned by a call to stat(2) for fpath. typeflag is an integer that has one of the following values:

FTW_F
fpath is a normal 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.

If fpath is a symbolic link and stat(2) failed, POSIX.1-2001 states that it is undefined whether FTW_NS or FTW_SL (see below) is passed in typeflag.

To stop the tree walk, fn() returns a non-zero 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 non-zero 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.

This flags argument is formed by ORing zero or more of the following flags:

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 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.

If FTW_PHYS is not set, but FTW_DEPTH is set, then the function fn() is never called for a directory that would be a descendant of itself.

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.

If fn() returns non-zero, then the tree walk is terminated and the value returned by fn() is returned as the result of ftw() or nftw().

If nftw() is called with the FTW_ACTIONRETVAL flag, then the only non-zero value that should be used by fn() to terminate the tree walk is FTW_STOP, and that value is returned as the result of nftw().

NOTES

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.

CONFORMING TO

POSIX.1-2001, SVr4, SUSv1.

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>
 
 static int
 display_info(const char *fpath, const struct stat *sb, 
              int tflag, struct FTW *ftwbuf)
 {
     printf("%-3s %2d %7lld   %-40s %d %s\n",
         (tflag == FTW_D) ?   "d"   : (tflag == FTW_DNR) ? "dnr" :
         (tflag == FTW_DP) ?  "dp"  : (tflag == FTW_F) ?   "f" :
         (tflag == FTW_DP) ?  "dp"  : (tflag == FTW_SL) ?  "sl" :
         (tflag == FTW_SLN) ? "sln" : "???",
         ftwbuf->level, (long long) 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;
 
     nftw((argc < 2) ? "." : argv[1], display_info, 20, flags);
     exit(EXIT_SUCCESS);
 }

SEE ALSO

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