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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
       #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 (pre-order 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
       relative to dirpath.  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 non-zero 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 non-zero 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 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 file system	(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  non-zero,  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  non-
       zero  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
       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), feature_test_macros(7)

COLOPHON
       This  page  is  part of release 3.22 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				  2008-08-06				FTW(3)
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