PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       ftw — traverse (walk) a file tree

SYNOPSIS

       #include <ftw.h>

       int ftw(const char *path, int (*fn)(const char *,
           const struct stat *ptr, int flag), int ndirs);

DESCRIPTION

       The  ftw() function shall recursively descend the directory hierarchy rooted in path.  For each object in
       the hierarchy, ftw() shall call the function pointed to by fn, passing it a pointer to a  null-terminated
       character  string containing the name of the object, a pointer to a stat structure containing information
       about the object, filled in as if stat() or lstat() had been called to retrieve the information. Possible
       values of the integer, defined in the <ftw.h> header, are:

       FTW_D     For a directory.

       FTW_DNR   For a directory that cannot be read.

       FTW_F     For a non-directory file.

       FTW_SL    For a symbolic link (but see also FTW_NS below).

       FTW_NS    For an object other than a symbolic link on which stat() could not successfully be executed. If
                 the object is a symbolic link and stat() failed, it is unspecified whether ftw() passes  FTW_SL
                 or FTW_NS to the user-supplied function.

       If  the  integer  is  FTW_DNR,  descendants  of  that directory shall not be processed. If the integer is
       FTW_NS, the stat structure contains undefined values. An example of an object that would cause FTW_NS  to
       be  passed  to the function pointed to by fn would be a file in a directory with read but without execute
       (search) permission.

       The ftw() function shall visit a directory before visiting any of its descendants.

       The ftw() function shall use at most one file descriptor for each level in the tree.

       The argument ndirs should be in the range [1,{OPEN_MAX}].

       The tree traversal shall continue until either the tree is exhausted, an invocation of fn returns a  non-
       zero value, or some error, other than [EACCES], is detected within ftw().

       The  ndirs  argument  shall  specify  the maximum number of directory streams or file descriptors or both
       available for use by ftw() while traversing the tree. When ftw() returns it  shall  close  any  directory
       streams and file descriptors it uses not counting any opened by the application-supplied fn function.

       The results are unspecified if the application-supplied fn function does not preserve the current working
       directory.

       The ftw() function need not be thread-safe.

RETURN VALUE

       If the tree is exhausted, ftw() shall return 0. If the function pointed  to  by  fn  returns  a  non-zero
       value, ftw() shall stop its tree traversal and return whatever value was returned by the function pointed
       to by fn.  If ftw() detects an error, it shall return −1 and set errno to indicate the error.

       If ftw() encounters an error other than [EACCES] (see FTW_DNR and FTW_NS above), it shall return  −1  and
       set errno to indicate the error. The external variable errno may contain any error value that is possible
       when a directory is opened or when one of the stat functions is executed on a directory or file.

ERRORS

       The ftw() function shall fail if:

       EACCES Search permission is denied for any component of path or read permission is denied for path.

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

       ENAMETOOLONG
              The length of a component of a pathname is longer than {NAME_MAX}.

       ENOENT A component of path does not name an existing file or path is an empty string.

       ENOTDIR
              A component of path names an existing file that is neither a directory nor a symbolic  link  to  a
              directory.

       EOVERFLOW
              A  field  in  the  stat  structure  cannot  be  represented  correctly  in the current programming
              environment for one or more files found in the file hierarchy.

       The ftw() function may fail if:

       EINVAL The value of the ndirs argument is invalid.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

       ENAMETOOLONG
              The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an
              intermediate result with a length that exceeds {PATH_MAX}.

       In addition, if the function pointed to by fn encounters system errors, errno may be set accordingly.

       The following sections are informative.

EXAMPLES

   Walking a Directory Structure
       The  following example walks the current directory structure, calling the fn function for every directory
       entry, using at most 10 file descriptors:

           #include <ftw.h>
           ...
           if (ftw(".", fn, 10) != 0) {
               perror("ftw"); exit(2);
           }

APPLICATION USAGE

       The ftw() function may allocate dynamic storage during its operation. If ftw()  is  forcibly  terminated,
       such  as  by  longjmp()  or  siglongjmp() being executed by the function pointed to by fn or an interrupt
       routine, ftw() does not have a chance to free that storage, so it remains permanently allocated.  A  safe
       way  to  handle  interrupts  is to store the fact that an interrupt has occurred, and arrange to have the
       function pointed to by fn return a non-zero value at its next invocation.

       Applications should use the nftw() function instead of the obsolescent ftw() function.

RATIONALE

       None.

FUTURE DIRECTIONS

       The ftw() function may be removed in a future version.

SEE ALSO

       fdopendir(), fstatat(), longjmp(), nftw(), siglongjmp()

       The Base Definitions volume of POSIX.1‐2008, <ftw.h>, <sys_stat.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event
       of any discrepancy between this version and the original IEEE and The Open Group Standard,  the  original
       IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at
       http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .