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.
       typeflag 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.)

       The  fourth argument that nftw() supplies when calling fn() is a struc-
       ture 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().

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 4.10 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/.



Linux				  2017-03-13				FTW(3)