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

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   /* See feature_test_macros(7) */
       #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 direc‐
       tory 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 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 argu‐
       ments: fpath, sb, and typeflag.	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 ftw(), 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_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 nonzero 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 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.

   nftw()
       The function nftw() is the same as ftw(), except that it has one	 addi‐
       tional 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	 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.

       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.

       For each entry in the directory tree, nftw() calls fn() with four argu‐
       ments.  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  pro‐
	      cessed.

       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).

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().

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

NOTES
       POSIX.1-2001 note 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.

       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.

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().

       #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);
       }

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

COLOPHON
       This page is part of release 3.54 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2010-09-20				FTW(3)
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