ftw, nftw — file tree walk
#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); |
#include <ftw.h>
int
ftw( |
const char *dirpath, |
int (*fn)(const char *fpath,
const struct stat *sb, int typeflag), |
|
int nopenfd); |
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Note | ||
|---|---|---|---|
|
nftw() 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).
To avoid using up all of the calling process's file
descriptors, nopenfd
specifies the maximum number of directories that nftw() will hold open simultaneously. When
the search depth exceeds this, nftw() will become slower because
directories have to be closed and reopened. nftw() uses at most one file descriptor for
each level in the directory tree.
For each entry found in the tree, nftw() calls fn() with four arguments: fpath, sb, typeflag, and ftwbuf. fpath is the pathname of the
entry, and is expressed either as a pathname relative to the
calling process's current working directory at the time of
the call to nftw(), if
dirpath was expressed
as a relative pathname, or as an absolute pathname, if
dirpath was expressed
as an absolute pathname. 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_Ffpath is a
regular file.
FTW_Dfpath is a
directory.
FTW_DNRfpath is a
directory which can't be read.
FTW_DPfpath is a
directory, and FTW_DEPTH
was specified in flags. (If FTW_DEPTH was not specified in
flags, then
directories will always be visited with typeflag set to
FTW_D.) All of the files
and subdirectories within fpath have been
processed.
FTW_NSThe stat(2) call failed
on fpath, which
is not a symbolic link. The probable cause for this is
that the caller had read permission on the parent
directory, so that the filename fpath could be seen, but
did not have execute permission, so that the file could
not be reached for stat(2).
FTW_SLfpath is a
symbolic link, and FTW_PHYS was set in flags.
FTW_SLNfpath 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).
To stop the tree walk, fn()
returns a nonzero value; this value will become the return
value of nftw(). As long as
fn() returns 0, nftw() 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 nftw() 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.
The flags argument
of nftw() 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_CONTINUEInstructs
nftw() to continue normally.FTW_SKIP_SIBLINGSIf
fn() returns this value, then siblings of the current entry will be skipped, and processing continues in the parent.FTW_SKIP_SUBTREEIf
fn() is called with an entry that is a directory (typeflagisFTW_D), this return value will prevent objects within that directory from being passed as arguments tofn().nftw() continues processing with the next sibling of the directory.FTW_STOPCauses
nftw() to return immediately with the return valueFTW_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_SOURCEmust be defined (before includinganyheader files) in order to obtain the definition ofFTW_ACTIONRETVALfrom<ftw.h>
FTW_CHDIRIf 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.
(Specifying this flag has no effect on the pathname
that is passed in the fpath argument of
fn.)
FTW_DEPTHIf 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_MOUNTIf set, stay within the same filesystem (i.e., do not cross mount points).
FTW_PHYSIf 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.
ftw() is an older function
that offers a subset of the functionality of nftw(). The notable differences are as
follows:
ftw() has no
flags
argument. It behaves the same as when nftw() is called with flags specified as
zero.
The callback function, fn(), is not supplied
with a fourth argument.
The range of values that is passed via the
typeflag
argument supplied to fn() is smaller: just
FTW_F, FTW_D, FTW_DNR, FTW_NS, and (possibly) FTW_SL.
These functions return 0 on success, and −1 if an error occurs.
If fn() returns nonzero,
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 nonzero 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().
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
nftw() |
Thread safety | MT-Safe cwd |
ftw() |
Thread safety | MT-Safe |
POSIX.1-2008 notes 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.
In some implementations (e.g., glibc), 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. If
fpath is a symbolic
link and stat(2) failed,
POSIX.1-2008 states that it is undefined whether FTW_NS or FTW_SL is passed in typeflag. For predictable
results, use nftw().
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);
}
This page is part of release 4.00 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
http://www.kernel.org/doc/man−pages/.
|
Copyright (c) 1993 Michael Haardt (michaelmoria.de) and copyright (c) 1999 Andries Brouwer (aebcwi.nl) and copyright (c) 2006 Justin Pryzby <justinpryzbyusers.sf.net> and copyright (c) 2006 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(GPLv2+_DOC_FULL) This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, see <http://www.gnu.org/licenses/>. %%%LICENSE_END Modified Sun Jul 25 11:02:22 1993 by Rik Faith (faithcs.unc.edu) 2006-05-24, Justin Pryzby <justinpryzbyusers.sf.net> document FTW_ACTIONRETVAL; include .SH RETURN VALUE; 2006-05-24, Justin Pryzby <justinpryzbyusers.sf.net> and Michael Kerrisk <mtk.manpagesgmail.com> reorganized and rewrote much of the page 2006-05-24, Michael Kerrisk <mtk.manpagesgmail.com> Added an example program. |