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       ftw, nftw - file tree walk


       #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);


       ftw()  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 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

       For  each  entry  found  in  the  tree,  ftw()  calls  fn()  with three
       arguments: 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.

              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().   Dont use
       longjmp(3) unless the program is going to terminate.

       The function nftw() is the same  as  ftw(),  except  that  it  has  one
       additional  argument,  flags,  and  calls  fn() with one more argument,

       This flags argument is formed by ORing zero or more  of  the  following

       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 current
                     entry will be skipped, and processing  continues  in  the

                     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

              Other return values could be associated with new actions in  the
              future;  fn()  should  not return values other than those listed

              The feature test macro _GNU_SOURCE must be defined 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.

              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.)

              If set, stay within the same file system  (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

              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
       arguments.  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

       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.)

       The fourth argument  that  nftw()  supplies  when  calling  fn()  is  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).


       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().


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


       The function nftw() and the use of FTW_SL with ftw() were introduced in

       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.


       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().

       #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 */

       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) {


       stat(2), fts(3), readdir(3), feature_test_macros(7)


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