FTW(3)                              Linux Programmer's Manual                              FTW(3)



NAME
       ftw, nftw - file tree walk

SYNOPSIS
       #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   /* See feature_test_macros(7) */
       #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);

DESCRIPTION
       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 tree.

       For each entry found in the tree, ftw() calls fn() with three arguments:  fpath,  sb,  and
       typeflag.  fpath is the pathname of the entry, and is expressed either as a pathname rela‐
       tive to the calling process's current working directory at the time of the call to  ftw(),
       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.

       FTW_DNR
              fpath is a directory which can't be read.

       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).

              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  tra‐
       versed 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().   Don't
       use longjmp(3) unless the program is going to terminate.

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

       This flags argument 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:

              FTW_CONTINUE
                     Instructs nftw() to continue normally.

              FTW_SKIP_SIBLINGS
                     If  fn()  returns  this  value,  then  siblings of the current entry will be
                     skipped, and processing continues in the parent.

              FTW_SKIP_SUBTREE
                     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 sib‐
                     ling of the directory.

              FTW_STOP
                     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>.

       FTW_CHDIR
              If set, do a chdir(2) to each directory before handling its contents.  This is use‐
              ful if the program needs to perform some action in the  directory  in  which  fpath
              resides.

       FTW_DEPTH
              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.)

       FTW_MOUNT
              If set, stay within the same filesystem (i.e., do not cross mount points).

       FTW_PHYS
              If  set,  do not follow symbolic links.  (This is what you want.)  If not set, sym‐
              bolic 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.

       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.  (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_SL fpath is a symbolic link, and FTW_PHYS was set in flags.

       FTW_SLN
              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).

RETURN VALUE
       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().

VERSIONS
       nftw() is available under glibc since version 2.1.

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

NOTES
       POSIX.1-2001  note  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.

       On some systems ftw() will never use FTW_SL, on other systems FTW_SL occurs only for  sym‐
       bolic  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().

       FTW_F is returned for all objects (files,  symbolic  links,  FIFOs,  etc.)   that  can  be
       stat'ed but are not a directory.

       FTW_ACTIONRETVAL is glibc-specific.

EXAMPLE
       The  following program traverses the directory tree under the path named in its first com‐
       mand-line argument, or under the current directory if no argument is  supplied.   It  dis‐
       plays  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 */
       }

       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);
       }

SEE ALSO
       stat(2), fts(3), readdir(3)

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-08-19                                     FTW(3)