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       ftw, nftw - file tree walk


       #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


       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

       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.  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_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).

       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).

       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  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 (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 handled
              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

              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() 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
          supplied to fn() is smaller: just FTW_F, FTW_D, FTW_DNR, FTW_NS, and
          (possibly) FTW_SL.


       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().


       nftw() is available under glibc since version 2.1.


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

       │InterfaceAttributeValue       │
       │nftw()    │ Thread safety │ MT-Safe cwd │
       │ftw()     │ Thread safety │ MT-Safe     │


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


       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

       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().


       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 %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)


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