nftw

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);

       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
       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 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 arguments:
       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 always
              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 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).  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 argument
              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 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 (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 useful if the program needs to perform some
              action 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 supplied
          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 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.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(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
       preserve 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 information
       about the dangling symbolic link (obtained by calling lstat(2) on the
       link).  Early glibc versions correctly followed the POSIX specification
       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 undefined when
       FTW_SLN is passed in typeflag.  (More precisely, the contents 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 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 ",
                   (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
       This page is part of release 5.13 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
       https://www.kernel.org/doc/man-pages/.




Linux                              2021-03-22                             FTW(3)