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PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       nftw — walk a file tree

SYNOPSIS

       #include <ftw.h>

       int nftw(const char *path, int (*fn)(const char *,
           const struct stat *, int, struct FTW *), int fd_limit, int flags);

DESCRIPTION

       The nftw() function shall recursively descend the directory hierarchy rooted in path.  The
       nftw() function has a similar effect to ftw() except that it takes an additional  argument
       flags, which is a bitwise-inclusive OR of zero or more of the following flags:

       FTW_CHDIR   If set, nftw() shall change the current working directory to each directory as
                   it reports files in that directory. If clear,  nftw()  shall  not  change  the
                   current working directory.

       FTW_DEPTH   If  set,  nftw()  shall  report  all files in a directory before reporting the
                   directory itself. If clear, nftw() shall report any directory before reporting
                   the files in that directory.

       FTW_MOUNT   If  set,  nftw()  shall only report files in the same file system as path.  If
                   clear, nftw() shall report all files encountered during the walk.

       FTW_PHYS    If set, nftw() shall perform a physical walk and  shall  not  follow  symbolic
                   links.

       If  FTW_PHYS is clear and FTW_DEPTH is set, nftw() shall follow links instead of reporting
       them, but shall not report any directory that would be a descendant of itself. If FTW_PHYS
       is  clear and FTW_DEPTH is clear, nftw() shall follow links instead of reporting them, but
       shall not report the contents of any directory that would be a descendant of itself.

       At each file it encounters, nftw() shall call the  user-supplied  function  fn  with  four
       arguments:

        *  The first argument is the pathname of the object.

        *  The  second  argument  is  a  pointer to the stat buffer containing information on the
           object, filled in as if fstatat(), stat(), or lstat() had been called to retrieve  the
           information.

        *  The  third  argument  is an integer giving additional information. Its value is one of
           the following:

           FTW_D     The object is a directory.

           FTW_DNR   The object is a directory that cannot be read. The fn function shall not  be
                     called for any of its descendants.

           FTW_DP    The  object  is  a  directory  and  subdirectories  have been visited. (This
                     condition shall only occur if the FTW_DEPTH flag is included in flags.)

           FTW_F     The object is a non-directory file.

           FTW_NS    The stat() function failed on the object  because  of  lack  of  appropriate
                     permission. The stat buffer passed to fn is undefined. Failure of stat() for
                     any other reason is considered an error and nftw() shall return -1.

           FTW_SL    The object is a symbolic link. (This  condition  shall  only  occur  if  the
                     FTW_PHYS flag is included in flags.)

           FTW_SLN   The  object  is  a symbolic link that does not name an existing file.  (This
                     condition shall only occur if the FTW_PHYS flag is not included in flags.)

        *  The fourth argument is a pointer to an FTW structure.  The value of base is the offset
           of  the  object's  filename  in  the pathname passed as the first argument to fn.  The
           value of level indicates depth relative to the root of the walk, where the root  level
           is 0.

       The  results are unspecified if the application-supplied fn function does not preserve the
       current working directory.

       The argument fd_limit sets the maximum number of file descriptors that shall  be  used  by
       nftw()  while traversing the file tree. At most one file descriptor shall be used for each
       directory level.

       The nftw() function need not be thread-safe.

RETURN VALUE

       The nftw() function shall continue until the first of the following conditions occurs:

        *  An invocation of fn shall return a non-zero value, in which case nftw()  shall  return
           that value.

        *  The  nftw()  function  detects  an  error  other than [EACCES] (see FTW_DNR and FTW_NS
           above), in which case nftw() shall return -1 and set errno to indicate the error.

        *  The tree is exhausted, in which case nftw() shall return 0.

ERRORS

       The nftw() function shall fail if:

       EACCES Search permission is denied for any component of path or read permission is  denied
              for path, or fn returns -1 and does not reset errno.

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

       ENAMETOOLONG
              The length of a component of a pathname is longer than {NAME_MAX}.

       ENOENT A component of path does not name an existing file or path is an empty string.

       ENOTDIR
              A  component  of  path  names  an  existing  file that is neither a directory nor a
              symbolic link to a directory.

       EOVERFLOW
              A field in the stat structure  cannot  be  represented  correctly  in  the  current
              programming environment for one or more files found in the file hierarchy.

       The nftw() function may fail if:

       ELOOP  More  than  {SYMLOOP_MAX}  symbolic links were encountered during resolution of the
              path argument.

       EMFILE All file descriptors available to the process are currently open.

       ENAMETOOLONG
              The length of a pathname exceeds {PATH_MAX}, or pathname resolution of  a  symbolic
              link produced an intermediate result with a length that exceeds {PATH_MAX}.

       ENFILE Too many files are currently open in the system.

       In addition, errno may be set if the function pointed to by fn causes errno to be set.

       The following sections are informative.

EXAMPLES

       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().

           #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) ?
                       (S_ISBLK(sb->st_mode) ? "f b" :
                        S_ISCHR(sb->st_mode) ? "f c" :
                        S_ISFIFO(sb->st_mode) ? "f p" :
                        S_ISREG(sb->st_mode) ? "f r" :
                        S_ISSOCK(sb->st_mode) ? "f s" : "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);
           }

APPLICATION USAGE

       The  nftw()  function  may  allocate  dynamic  storage  during its operation. If nftw() is
       forcibly terminated, such as by longjmp() or siglongjmp() being executed by  the  function
       pointed  to  by  fn  or  an  interrupt routine, nftw() does not have a chance to free that
       storage, so it remains permanently allocated. A safe way to handle interrupts is to  store
       the fact that an interrupt has occurred, and arrange to have the function pointed to by fn
       return a non-zero value at its next invocation.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       fdopendir(), fstatat(), readdir()

       The Base Definitions volume of POSIX.1‐2017, <ftw.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  by
       the  Institute  of  Electrical  and Electronics Engineers, Inc and The Open Group.  In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .