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
       #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 direc-
       tory dirpath, and calls fn() once for  each  entry  in  the  tree.   By
       default,  directories  are  handled before the files and subdirectories
       they contain (pre-order 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 argu-
       ments: fpath, sb, and typeflag.  fpath is the  pathname  of  the  entry
       relative to dirpath.  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 normal 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.

              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 non-zero value; this  value  will
       become  the  return  value  of ftw().  As long as fn() returns 0, ftw()
       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 ftw() uses dynamic data structures, the only safe way  to  exit
       out of a tree walk is to return a non-zero 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  addi-
       tional  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 argu-
                     ments to fn().  nftw() continues processing with the next
                     sibling 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 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 con-
              tents.  This is useful 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 file system  (i.e.,  do  not  cross
              mount points).

       FTW_PHYS
              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.

       For each entry in the directory tree, nftw() calls fn() with four argu-
       ments.  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.  All
              of the files and subdirectories  within  fpath  have  been  pro-
              cessed.

       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  struc-
       ture 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  non-zero,  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  non-
       zero  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().

NOTES
       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 symbolic 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().

       Under Linux, libc4 and libc5 and glibc 2.0.6 will  use  FTW_F  for  all
       objects (files, symbolic links, fifos, etc) that can be stat'ed but are
       not a directory.

       The function nftw() is available since glibc 2.1.

       FTW_ACTIONRETVAL is glibc specific.

CONFORMING TO
       POSIX.1-2001, SVr4, SUSv1.

EXAMPLE
       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 charac-
       ters that control the value assigned to the flags argument when calling
       nftw().

       #define _XOPEN_SOURCE 500
       #include <ftw.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       static int
       display_info(const char *fpath, const struct stat *sb,
                    int tflag, struct FTW *ftwbuf)
       {
           printf("%-3s %2d %7lld   %-40s %d %s\n",
               (tflag == FTW_D) ?   "d"   : (tflag == FTW_DNR) ? "dnr" :
               (tflag == FTW_DP) ?  "dp"  : (tflag == FTW_F) ?   "f" :
               (tflag == FTW_DP) ?  "dp"  : (tflag == FTW_SL) ?  "sl" :
               (tflag == FTW_SLN) ? "sln" : "???",
               ftwbuf->level, (long long) 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;

           nftw((argc < 2) ? "." : argv[1], display_info, 20, flags);
           exit(EXIT_SUCCESS);
       }

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

Linux                             2006-05-24                            FTW(3)