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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 tree.

       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.

       The typeflag argument passed to fn() 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).  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.

              fpath  is  a  symbolic  link  pointing to a nonexistent file.  (This occurs only if
              FTW_PHYS is not set.)  On most implementations, in this case the sb argument passed
              to  fn() contains information returned by performing lstat(2) on the symbolic link.
              For the details on Linux, see BUGS.

       The fourth argument (ftwbuf) that nftw() supplies when calling fn()  is  a  pointer  to  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 parent.

                     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 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>.

              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 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()  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 attributes(7).

       │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 obsolete.


       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 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().


       In the specification of nftw(), POSIX.1 notes that when FTW_NS is passed as  the  typeflag
       argument  of  fn(),  then  the  contents  of  the buffer pointed to by the sb argument are
       undefined.  The standard makes no such statement for the case where FTW_SLN is  passed  in
       typeflag,  with  the  implication  that  the  contents  of the buffer pointed to by sb are
       defined.  And indeed this is the case on most implementations: the buffer pointed to by sb
       contains  the results produced by applying lstat(2) to the symbolic link.  In early glibc,
       the behavior was the same.  However, since glibc 2.4, the contents of the  buffer  pointed
       to  by  sb are undefined when FTW_SLN is passed in typeflag.  This change appears to be an
       unintended regression, but it is not (yet) clear if the behavior will be restored to  that
       provided in the original glibc implementation (and on other implementations).


       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 ",
                   (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" : "???",

           if (tflag == FTW_NS)
               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 */

       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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