nftw(3)



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

NAME
       ftw, nftw - file tree walk

SYNOPSIS
       #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

DESCRIPTION
       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
       tree.

       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.

       FTW_DNR
              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.

       FTW_SLN
              fpath is a symbolic link pointing to a nonexistent file.   (This
              occurs  only if FTW_PHYS is not set.)  In this case the sb argu-
              ment passed to fn() contains information returned by  performing
              lstat(2) on the "dangling" symbolic link.  (But 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:

              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  ob-
                     jects  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  (before  in-
              cluding  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 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.)

       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, 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.

   ftw()
       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.

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 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().

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

ATTRIBUTES
       For  an  explanation  of  the  terms  used  in  this  section,  see at-
       tributes(7).

       +----------+---------------+-------------+
       |Interface | Attribute     | Value       |
       +----------+---------------+-------------+
       |nftw()    | Thread safety | MT-Safe cwd |
       +----------+---------------+-------------+
       |ftw()     | Thread safety | MT-Safe     |
       +----------+---------------+-------------+

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

NOTES
       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
       SUSv1.

       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().

BUGS
       According to POSIX.1-2008, when the typeflag argument  passed  to  fn()
       contains  FTW_SLN,  the buffer pointed to by sb should contain informa-
       tion about the dangling symbolic link (obtained by calling lstat(2)  on
       the  link).  Early glibc versions correctly followed the POSIX specifi-
       cation on this point.  However, as a result of a regression  introduced
       in  glibc  2.4,  the contents of the buffer pointed to by sb were unde-
       fined when FTW_SLN is passed in typeflag.  (More  precisely,  the  con-
       tents of the buffer were left unchanged in this case.)  This regression
       was eventually fixed in glibc 2.30, so that  the  glibc  implementation
       (once more) follows the POSIX specification.

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  charac-
       ters 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 ",
                   (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);

           if (tflag == FTW_NS)
               printf("-------");
           else
               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 */
       }

       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
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       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

Linux                             2020-06-09                            FTW(3)

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