ftw(3) — Linux manual page


FTW(3)                    Linux Programmer's Manual                   FTW(3)

NAME         top

       ftw, nftw - file tree walk

SYNOPSIS         top

       #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         top

       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.

       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.

              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
              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).  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.

              fpath is a symbolic link pointing to a nonexistent file.
              (This occurs only if FTW_PHYS is not set.)  In this case the
              sb argument passed to fn() contains information returned by
              performing lstat(2) on the "dangling" symbolic link.  (But see

       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 direc‐
       tory tree, relative to the root of the tree (dirpath, which has depth

       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:

                     Instructs nftw() to continue normally.

                     If fn() returns this value, then siblings of the cur‐
                     rent entry will be skipped, and processing continues in
                     the parent.

                     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.

                     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>.

              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.  (Specifying
              this flag has no effect on the pathname that is passed in the
              fpath argument of fn.)

              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 han‐
              dled before its contents.)

              If set, stay within the same filesystem (i.e., do not cross
              mount points).

              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 func‐
              tion 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 argu‐

       *  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         top

       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         top

       nftw() is available under glibc since version 2.1.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface Attribute     Value       │
       │nftw()    │ Thread safety │ MT-Safe cwd │
       │ftw()     │ Thread safety │ MT-Safe     │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4, SUSv1.  POSIX.1-2008 marks ftw() as

NOTES         top

       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

BUGS         top

       According to POSIX.1-2008, when the typeflag argument passed to fn()
       contains FTW_SLN, the buffer pointed to by sb should contain
       information about the dangling symbolic link (obtained by calling
       lstat(2) on the link).  Early glibc versions correctly followed the
       POSIX specification on this point.  However, as a result of a
       regression introduced in glibc 2.4, the contents of the buffer
       pointed to by sb were undefined when FTW_SLN is passed in typeflag.
       (More precisely, the contents of the buffer were left unchanged in
       this case.)  This regression was eventually fixed in glibc 2.30, so
       that the glibc implementation (once more) follows the POSIX

EXAMPLES         top

       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().

   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" : "???",

           if (tflag == FTW_NS)
               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 */

       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) {


SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2020-06-09                           FTW(3)

Pages that refer to this page: fts(3)fts_children(3)fts_close(3)fts_open(3)fts_read(3)fts_set(3)readdir(3)