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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 directory 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 direc-
       tories 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 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 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.

              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 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 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 contents.  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  con-
              tents  of  the directory and its subdirectories.  (By default, each directory is handled before its con-
              tents.)

       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  fol-
              lowed, 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.  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  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().

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

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  pre-
       dictable 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.

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 characters 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>
       #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), feature_test_macros(7)

COLOPHON
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-08-06                            FTW(3)