FTW(3) Linux Programmer's Manual FTW(3)
NAME
ftw, nftw - file tree walk
SYNOPSIS
#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);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
nftw(): _XOPEN_SOURCE >= 500
DESCRIPTION
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 argu-
ments: 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.
The typeflag argument passed to fn() is an integer that has one of the
following values:
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_DP fpath 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_NS The stat(2) call failed on fpath, which is not a symbolic link.
The probable cause for this is that the caller had read permis-
sion 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). The contents of the buffer
pointed to by sb are undefined.
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.) On most implementations,
in this case the sb argument passed to fn() contains information
returned by performing lstat(2) on the symbolic link. For the
details on Linux, see BUGS.
The fourth argument (ftwbuf) that nftw() supplies when calling fn() is
a pointer to 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_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 argu-
ments 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 con-
tents. 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_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 filesystem (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.
ftw()
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 sup-
plied to fn() is smaller: just FTW_F, FTW_D, FTW_DNR, FTW_NS, and
(possibly) FTW_SL.
RETURN VALUE
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().
VERSIONS
nftw() is available under glibc since version 2.1.
ATTRIBUTES
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 |
+----------+---------------+-------------+
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, SUSv1. POSIX.1-2008 marks ftw() as
obsolete.
NOTES
POSIX.1-2008 notes that the results are unspecified if fn does not pre-
serve 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().
BUGS
In the specification of nftw(), POSIX.1 notes that when FTW_NS is
passed as the typeflag argument of fn(), then the contents of the buf-
fer pointed to by the sb argument are undefined. The standard makes no
such statement for the case where FTW_SLN is passed in typeflag, with
the implication that the contents of the buffer pointed to by sb are
defined. And indeed this is the case on most implementations: the buf-
fer pointed to by sb contains the results produced by applying lstat(2)
to the symbolic link. In early glibc, the behavior was the same. How-
ever, since glibc 2.4, the contents of the buffer pointed to by sb are
undefined when FTW_SLN is passed in typeflag. This change appears to
be an unintended regression, but it is not (yet) clear if the behavior
will be restored to that provided in the original glibc implementation
(and on other implementations).
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 charac-
ters that control the value assigned to the flags argument when calling
nftw().
Program source
#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 ",
(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);
if (tflag == FTW_NS)
printf("-------");
else
printf("%7jd", (intmax_t) sb->st_size);
printf(" %-40s %d %s\n",
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 4.15 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
https://www.kernel.org/doc/man-pages/.
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