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FTS(3)				   BSD Library Functions Manual 			   FTS(3)

NAME
     fts, fts_open, fts_read, fts_children, fts_set, fts_close -- traverse a file hierarchy

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/stat.h>
     #include <fts.h>

     FTS *
     fts_open(char * const *path_argv, int options,
	 int (*compar)(const FTSENT **, const FTSENT **));

     FTSENT *
     fts_read(FTS *ftsp);

     FTSENT *
     fts_children(FTS *ftsp, int options);

     int
     fts_set(FTS *ftsp, FTSENT *f, int options);

     int
     fts_close(FTS *ftsp);

DESCRIPTION
     The fts functions are provided for traversing UNIX file hierarchies.  A simple overview is
     that the fts_open() function returns a ``handle'' on a file hierarchy, which is then sup-
     plied to the other fts functions.	The function fts_read() returns a pointer to a structure
     describing one of the files in the file hierarchy.  The function fts_children() returns a
     pointer to a linked list of structures, each of which describes one of the files contained
     in a directory in the hierarchy.  In general, directories are visited two distinguishable
     times; in pre-order (before any of their descendants are visited) and in post-order (after
     all of their descendants have been visited).  Files are visited once.  It is possible to
     walk the hierarchy ``logically'' (ignoring symbolic links) or physically (visiting symbolic
     links), order the walk of the hierarchy or prune and/or re-visit portions of the hierarchy.

     Two structures are defined (and typedef'd) in the include file <fts.h>.  The first is FTS,
     the structure that represents the file hierarchy itself.  The second is FTSENT, the struc-
     ture that represents a file in the file hierarchy.  Normally, an FTSENT structure is
     returned for every file in the file hierarchy.  In this manual page, ``file'' and ``FTSENT
     structure'' are generally interchangeable.  The FTSENT structure contains at least the fol-
     lowing fields, which are described in greater detail below:

       typedef struct _ftsent {
	       u_short fts_info;	       /* flags for FTSENT structure */
	       char *fts_accpath;	       /* access path */
	       char *fts_path;		       /* root path */
	       short fts_pathlen;	       /* strlen(fts_path) */
	       char *fts_name;		       /* file name */
	       short fts_namelen;	       /* strlen(fts_name) */
	       short fts_level; 	       /* depth (-1 to N) */
	       int fts_errno;		       /* file errno */
	       long fts_number; 	       /* local numeric value */
	       void *fts_pointer;	       /* local address value */
	       struct ftsent *fts_parent;      /* parent directory */
	       struct ftsent *fts_link;        /* next file structure */
	       struct ftsent *fts_cycle;       /* cycle structure */
	       struct stat *fts_statp;	       /* stat(2) information */
       } FTSENT;

     These fields are defined as follows:

     fts_info	  One of the following flags describing the returned FTSENT structure and the
		  file it represents.  With the exception of directories without errors (FTS_D),
		  all of these entries are terminal, that is, they will not be revisited, nor
		  will any of their descendants be visited.

		  FTS_D        A directory being visited in pre-order.

		  FTS_DC       A directory that causes a cycle in the tree.  (The fts_cycle field
			       of the FTSENT structure will be filled in as well).

		  FTS_DEFAULT  Any FTSENT structure that represents a file type not explicitly
			       described by one of the other fts_info values.

		  FTS_DNR      A directory which cannot be read.  This is an error return, and
			       the fts_errno field will be set to indicate what caused the error.

		  FTS_DOT      A file named '.' or '..' which was not specified as a file name to
			       fts_open() (see FTS_SEEDOT).

		  FTS_DP       A directory being visited in post-order.  The contents of the
			       FTSENT structure will be unchanged from when it was returned in
			       pre-order, i.e., with the fts_info field set to FTS_D.

		  FTS_ERR      This is an error return, and the fts_errno field will be set to
			       indicate what caused the error.

		  FTS_F        A regular file.

		  FTS_NS       A file for which no stat(2) information was available.  The con-
			       tents of the fts_statp field are undefined.  This is an error
			       return, and the fts_errno field will be set to indicate what
			       caused the error.

		  FTS_NSOK     A file for which no stat(2) information was requested.  The con-
			       tents of the fts_statp field are undefined.

		  FTS_SL       A symbolic link.

		  FTS_SLNONE   A symbolic link with a non-existent target.  The contents of the
			       fts_statp field reference the file characteristic information for
			       the symbolic link itself.

		  FTS_W        A whiteout object.

     fts_accpath  A path for accessing the file from the current directory.

     fts_path	  The path for the file relative to the root of the traversal.	This path con-
		  tains the path specified to fts_open() as a prefix.

     fts_pathlen  The length of the string referenced by fts_path.

     fts_name	  The name of the file.

     fts_namelen  The length of the string referenced by fts_name.

     fts_level	  The depth of the traversal, numbered from -1 to N, where this file was found.
		  The FTSENT structure representing the parent of the starting point (or root) of
		  the traversal is numbered -1, and the FTSENT structure for the root itself is
		  numbered 0.

     fts_errno	  Upon return of a FTSENT structure from the fts_children() or fts_read() func-
		  tions, with its fts_info field set to FTS_DNR, FTS_ERR or FTS_NS, the fts_errno
		  field contains the value of the external variable errno specifying the cause of
		  the error.  Otherwise, the contents of the fts_errno field are undefined.

     fts_number   This field is provided for the use of the application program and is not modi-
		  fied by the fts functions.  It is initialized to 0.

     fts_pointer  This field is provided for the use of the application program and is not modi-
		  fied by the fts functions.  It is initialized to NULL.

     fts_parent   A pointer to the FTSENT structure referencing the file in the hierarchy immedi-
		  ately above the current file, i.e., the directory of which this file is a mem-
		  ber.	A parent structure for the initial entry point is provided as well, how-
		  ever, only the fts_level, fts_number and fts_pointer fields are guaranteed to
		  be initialized.

     fts_link	  Upon return from the fts_children() function, the fts_link field points to the
		  next structure in the NULL-terminated linked list of directory members.  Other-
		  wise, the contents of the fts_link field are undefined.

     fts_cycle	  If a directory causes a cycle in the hierarchy (see FTS_DC), either because of
		  a hard link between two directories, or a symbolic link pointing to a direc-
		  tory, the fts_cycle field of the structure will point to the FTSENT structure
		  in the hierarchy that references the same file as the current FTSENT structure.
		  Otherwise, the contents of the fts_cycle field are undefined.

     fts_statp	  A pointer to stat(2) information for the file.

     A single buffer is used for all of the paths of all of the files in the file hierarchy.
     Therefore, the fts_path and fts_accpath fields are guaranteed to be NULL-terminated only for
     the file most recently returned by fts_read().  To use these fields to reference any files
     represented by other FTSENT structures will require that the path buffer be modified using
     the information contained in that FTSENT structure's fts_pathlen field.  Any such modifica-
     tions should be undone before further calls to fts_read() are attempted.  The fts_name field
     is always NULL-terminated.

FTS_OPEN
     The fts_open() function takes a pointer to an array of character pointers naming one or more
     paths which make up a logical file hierarchy to be traversed.  The array must be terminated
     by a NULL pointer.

     There are a number of options, at least one of which (either FTS_LOGICAL or FTS_PHYSICAL)
     must be specified.  The options are selected by or'ing the following values:

     FTS_COMFOLLOW   This option causes any symbolic link specified as a root path to be followed
		     immediately whether or not FTS_LOGICAL is also specified.

     FTS_LOGICAL     This option causes the fts routines to return FTSENT structures for the tar-
		     gets of symbolic links instead of the symbolic links themselves.  If this
		     option is set, the only symbolic links for which FTSENT structures are
		     returned to the application are those referencing non-existent files.
		     Either FTS_LOGICAL or FTS_PHYSICAL must be provided to the fts_open() func-
		     tion.

     FTS_NOCHDIR     As a performance optimization, the fts functions change directories as they
		     walk the file hierarchy.  This has the side-effect that an application can-
		     not rely on being in any particular directory during the traversal.  The
		     FTS_NOCHDIR option turns off this optimization, and the fts functions will
		     not change the current directory.	Note that applications should not them-
		     selves change their current directory and try to access files unless
		     FTS_NOCHDIR is specified and absolute pathnames were provided as arguments
		     to fts_open().

     FTS_NOSTAT      By default, returned FTSENT structures reference file characteristic infor-
		     mation (the statp field) for each file visited.  This option relaxes that
		     requirement as a performance optimization, allowing the fts functions to set
		     the fts_info field to FTS_NSOK and leave the contents of the statp field
		     undefined.

     FTS_PHYSICAL    This option causes the fts routines to return FTSENT structures for symbolic
		     links themselves instead of the target files they point to.  If this option
		     is set, FTSENT structures for all symbolic links in the hierarchy are
		     returned to the application.  Either FTS_LOGICAL or FTS_PHYSICAL must be
		     provided to the fts_open() function.

     FTS_SEEDOT      By default, unless they are specified as path arguments to fts_open(), any
		     files named '.' or '..' encountered in the file hierarchy are ignored.  This
		     option causes the fts routines to return FTSENT structures for them.

     FTS_WHITEOUT    Return whiteout entries, which are normally hidden.

     FTS_XDEV	     This option prevents fts from descending into directories that have a dif-
		     ferent device number than the file from which the descent began.

     The argument compar() specifies a user-defined function which may be used to order the tra-
     versal of the hierarchy.  It takes two pointers to pointers to FTSENT structures as argu-
     ments and should return a negative value, zero, or a positive value to indicate if the file
     referenced by its first argument comes before, in any order with respect to, or after, the
     file referenced by its second argument.  The fts_accpath, fts_path and fts_pathlen fields of
     the FTSENT structures may never be used in this comparison.  If the fts_info field is set to
     FTS_NS or FTS_NSOK, the fts_statp field may not either.  If the compar() argument is NULL,
     the directory traversal order is in the order listed in path_argv for the root paths, and in
     the order listed in the directory for everything else.

FTS_READ
     The fts_read() function returns a pointer to an FTSENT structure describing a file in the
     hierarchy.  Directories (that are readable and do not cause cycles) are visited at least
     twice, once in pre-order and once in post-order.  All other files are visited at least once.
     (Hard links between directories that do not cause cycles or symbolic links to symbolic links
     may cause files to be visited more than once, or directories more than twice.)

     If all the members of the hierarchy have been returned, fts_read() returns NULL and sets the
     external variable errno to 0.  If an error unrelated to a file in the hierarchy occurs,
     fts_read() returns NULL and sets errno appropriately.  If an error related to a returned
     file occurs, a pointer to an FTSENT structure is returned, and errno may or may not have
     been set (see fts_info).

     The FTSENT structures returned by fts_read() may be overwritten after a call to fts_close()
     on the same file hierarchy stream, or, after a call to fts_read() on the same file hierarchy
     stream unless they represent a file of type directory, in which case they will not be over-
     written until after a call to fts_read() after the FTSENT structure has been returned by the
     function fts_read() in post-order.

FTS_CHILDREN
     The fts_children() function returns a pointer to an FTSENT structure describing the first
     entry in a NULL-terminated linked list of the files in the directory represented by the
     FTSENT structure most recently returned by fts_read().  The list is linked through the
     fts_link field of the FTSENT structure, and is ordered by the user-specified comparison
     function, if any.	Repeated calls to fts_children() will recreate this linked list.

     As a special case, if fts_read() has not yet been called for a hierarchy, fts_children()
     will return a pointer to the files in the logical directory specified to fts_open(), i.e.,
     the arguments specified to fts_open().  Otherwise, if the FTSENT structure most recently
     returned by fts_read() is not a directory being visited in pre-order, or the directory does
     not contain any files, fts_children() returns NULL and sets errno to zero.  If an error
     occurs, fts_children() returns NULL and sets errno appropriately.

     The FTSENT structures returned by fts_children() may be overwritten after a call to
     fts_children(), fts_close() or fts_read() on the same file hierarchy stream.

     Option may be set to the following value:

     FTS_NAMEONLY    Only the names of the files are needed.  The contents of all the fields in
		     the returned linked list of structures are undefined with the exception of
		     the fts_name and fts_namelen fields.

FTS_SET
     The function fts_set() allows the user application to determine further processing for the
     file f of the stream ftsp.  The fts_set() function returns 0 on success, and -1 if an error
     occurs.  Option must be set to one of the following values:

     FTS_AGAIN	     Re-visit the file; any file type may be re-visited.  The next call to
		     fts_read() will return the referenced file.  The fts_stat and fts_info
		     fields of the structure will be reinitialized at that time, but no other
		     fields will have been changed.  This option is meaningful only for the most
		     recently returned file from fts_read().  Normal use is for post-order direc-
		     tory visits, where it causes the directory to be re-visited (in both pre and
		     post-order) as well as all of its descendants.

     FTS_FOLLOW      The referenced file must be a symbolic link.  If the referenced file is the
		     one most recently returned by fts_read(), the next call to fts_read()
		     returns the file with the fts_info and fts_statp fields reinitialized to
		     reflect the target of the symbolic link instead of the symbolic link itself.
		     If the file is one of those most recently returned by fts_children(), the
		     fts_info and fts_statp fields of the structure, when returned by fts_read(),
		     will reflect the target of the symbolic link instead of the symbolic link
		     itself.  In either case, if the target of the symbolic link does not exist
		     the fields of the returned structure will be unchanged and the fts_info
		     field will be set to FTS_SLNONE.

		     If the target of the link is a directory, the pre-order return, followed by
		     the return of all of its descendants, followed by a post-order return, is
		     done.

     FTS_SKIP	     No descendants of this file are visited.  The file may be one of those most
		     recently returned by either fts_children() or fts_read().

FTS_CLOSE
     The fts_close() function closes a file hierarchy stream ftsp and restores the current direc-
     tory to the directory from which fts_open() was called to open ftsp.  The fts_close() func-
     tion returns 0 on success, and -1 if an error occurs.

ERRORS
     The function fts_open() may fail and set errno for any of the errors specified for the
     library functions open(2) and malloc(3).

     The function fts_close() may fail and set errno for any of the errors specified for the
     library functions chdir(2) and close(2).

     The functions fts_read() and fts_children() may fail and set errno for any of the errors
     specified for the library functions chdir(2), malloc(3), opendir(3), readdir(3) and stat(2).

     In addition, fts_children(), fts_open() and fts_set() may fail and set errno as follows:

     [EINVAL]		The options were invalid.

SEE ALSO
     find(1), chdir(2), stat(2), qsort(3), symlink(7)

STANDARDS
     The fts utility was expected to be included in the IEEE Std 1003.1-1988 (``POSIX.1'') revi-
     sion.  But twenty years later, it still was not included in the IEEE Std 1003.1-2008
     (``POSIX.1'') revision.

BSD					  March 30, 2011				      BSD
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