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man:ftw

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
     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 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
            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 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.)  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
            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  (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 con-
            tents.   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 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
     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 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

     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
     buffer 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
     buffer  pointed  to  by  sb  contains  the results produced by applying
     lstat(2) to the symbolic link.  In early glibc, the  behavior  was  the
     same.   However, 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).

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().
 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 4.16 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 2017-09-15 FTW(3)

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