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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.  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 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().


       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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