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

       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 di-
       rectory 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

       For  each  entry  found  in the tree, nftw() calls fn() with four argu-
       ments: 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.

       The  typeflag argument passed to fn() 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 al-
              ways 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  permis-
              sion  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).  The contents of the buffer
              pointed to by sb are undefined.

       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.)  On most implementations,
              in this case the sb argument passed to fn() contains information
              returned  by  performing lstat(2) on the symbolic link.  For the
              details on Linux, see BUGS.

       The fourth argument (ftwbuf) that nftw() supplies when calling fn()  is
       a pointer to 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  re-
              turn 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

                     If fn() is called with  an  entry  that  is  a  directory
                     (typeflag  is  FTW_D), this return value will prevent ob-
                     jects within that directory from being  passed  as  argu-
                     ments to fn().  nftw() continues processing with the next
                     sibling of the directory.

                     Causes nftw() to return immediately with the return value

              Other  return values could be associated with new actions in the
              future; fn() should not return values other  than  those  listed

              The  feature  test macro _GNU_SOURCE must be defined (before in-
              cluding 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 con-
              tents.  This is useful if the program needs to perform some  ac-
              tion  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

              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 sup-
          plied 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  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().

       nftw() is available under glibc since version 2.1.

       For an  explanation  of  the  terms  used  in  this  section,  see  at-

       |Interface | Attribute     | Value       |
       |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

       POSIX.1-2008 notes that the results are unspecified if fn does not pre-
       serve the current working directory.

       The function nftw() and the use of FTW_SL with ftw() were introduced in

       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().

       In  the  specification  of  nftw(),  POSIX.1  notes that when FTW_NS is
       passed as the typeflag argument of fn(), then the contents of the  buf-
       fer pointed to by the sb argument are undefined.  The standard makes no
       such statement for the case where FTW_SLN is passed in  typeflag,  with
       the  implication  that  the contents of the buffer pointed to by sb are
       defined.  And indeed this is the case on most implementations: the buf-
       fer pointed to by sb contains the results produced by applying lstat(2)
       to the symbolic link.  In early glibc, the behavior was the same.  How-
       ever,  since glibc 2.4, the contents of the buffer pointed to by sb are
       undefined when FTW_SLN is passed in typeflag.  This change  appears  to
       be  an unintended regression, but it is not (yet) clear if the behavior
       will be restored to that provided in the original glibc  implementation
       (and on other implementations).

       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

   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 ",
                   (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" : "???",

           if (tflag == FTW_NS)
               printf("%7jd", (intmax_t) sb->st_size);

           printf("   %-40s %d %s\n",
                   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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