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



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

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 instr);

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

       int fts_close(FTS *ftsp);

DESCRIPTION
       The fts functions are provided for traversing file hierarchies.	A sim-
       ple  overview  is  that	the fts_open() function returns a "handle" (of
       type FTS *) that refers to a file hierarchy "stream".  This  handle  is
       then  supplied  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  postorder
       (after  all of their descendants have been visited).  Files are visited
       once.  It is possible to walk the hierarchy "logically"	(visiting  the
       files  that  symbolic  links point to) or physically (visiting the sym-
       bolic links themselves), order the  walk	 of  the  hierarchy  or	 prune
       and/or revisit portions of the hierarchy.

       Two  structures	(and associated types) are defined in the include file
       <fts.h>.	 The first type is FTS, the structure that represents the file
       hierarchy itself.  The second type is FTSENT, the structure that repre-
       sents 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 fields describing a file.	The  structure
       contains	 at  least  the	 following fields (there are additional fields
       that should be considered private to the implementation):

	   typedef struct _ftsent {
	       unsigned 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;     /* filename */
	       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 values 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 preorder.

		   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 speci-
			       fied  as a filename to fts_open() (see FTS_SEE-
			       DOT).

		   FTS_DP      A directory being visited  in  postorder.   The
			       contents	  of  the  FTSENT  structure  will  be
			       unchanged from when it  was  returned  in  pre-
			       order,  that is, 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 contents 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 contents of the fts_statp field
			       are undefined.

		   FTS_SL      A symbolic link.

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

       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 traver-
		   sal.	 This path contains 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   If fts_children() or fts_read() returns an FTSENT structure
		   whose fts_info field is set to FTS_DNR, FTS_ERR, or FTS_NS,
		   the	fts_errno  field  contains the error number (i.e., the
		   errno value) 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 pro-
		   gram and is not modified by the fts functions.  It is  ini-
		   tialized to 0.

       fts_pointer This	 field is provided for the use of the application pro-
		   gram and is not modified by the fts functions.  It is  ini-
		   tialized to NULL.

       fts_parent  A  pointer  to the FTSENT structure referencing the file in
		   the hierarchy immediately above the current file, that  is,
		   the	directory  of  which  this file is a member.  A parent
		   structure for the initial entry point is provided as	 well,
		   however,  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.  Otherwise, 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 directo-
		   ries,  or  a	 symbolic  link	 pointing  to a directory, 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 buf-
       fer be modified using the information contained in that	FTSENT	struc-
       ture's  fts_pathlen  field.   Any  such	modifications 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 point-
       ers 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_LOGI-
       CAL or FTS_PHYSICAL) must be specified.	The options  are  selected  by
       ORing the following values:

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

       FTS_LOGICAL   This  option  causes  the	fts  routines to return FTSENT
		     structures for the targets 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 nonex-
		     istent files.  Either FTS_LOGICAL or FTS_PHYSICAL must be
		     provided to the fts_open() function.

       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 cannot 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 themselves change their
		     current  directory	 and  try  to  access	files	unless
		     FTS_NOCHDIR is specified and absolute pathnames were pro-
		     vided as arguments to fts_open().

       FTS_NOSTAT    By default, returned  FTSENT  structures  reference  file
		     characteristic  information  (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_XDEV	     This option prevents fts from descending into directories
		     that have a different 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 traversal of the hierarchy.  It takes two pointers to
       pointers to FTSENT structures as arguments 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	 preorder  and
       once  in	 postorder.  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 direc-
       tories 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  overwritten
       until  after  a	call to fts_read() after the FTSENT structure has been
       returned by the function fts_read() in postorder.

   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_chil-
       dren() will re-create this linked list.

       As a special case, if fts_read() has not yet been called for a  hierar-
       chy,  fts_children()  will return a pointer to the files in the logical
       directory specified to fts_open(), that is, the arguments specified  to
       fts_open().   Otherwise, if the FTSENT structure most recently returned
       by fts_read() is not a directory being  visited	in  preorder,  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.

       The instr argument is either zero or 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.

       The instr argument is either 0 (meaning "do nothing")  or  one  of  the
       following values:

       FTS_AGAIN    Revisit  the  file;	 any  file type may be revisited.  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
		    postorder  directory visits, where it causes the directory
		    to be revisited (in both preorder and postorder)  as  well
		    as all of its descendants.

       FTS_FOLLOW   The	 referenced file must be a symbolic link.  If the ref-
		    erenced  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 preorder
		    return, followed by the return of all of its  descendants,
		    followed by a postorder 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_chil-
		    dren() or fts_read().

   fts_close()
       The  fts_close()	 function closes the file hierarchy stream referred to
       by ftsp and restores the current directory to the directory from	 which
       fts_open() was called to open ftsp.  The fts_close() function 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 open(2) and malloc(3).

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

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

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

       EINVAL options or instr was invalid.

VERSIONS
       These functions are available in Linux since glibc2.

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

       +-----------------------------------+---------------+-----------+
       |Interface			   | Attribute	   | Value     |
       +-----------------------------------+---------------+-----------+
       |fts_open(), fts_set(), fts_close() | Thread safety | MT-Safe   |
       +-----------------------------------+---------------+-----------+
       |fts_read(), fts_children()	   | Thread safety | MT-Unsafe |
       +-----------------------------------+---------------+-----------+

CONFORMING TO
       4.4BSD.

BUGS
       In versions of glibc before 2.23, all of the APIs described in this man
       page  are  not  safe when compiling a program using the LFS APIs (e.g.,
       when compiling with -D_FILE_OFFSET_BITS=64).

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

COLOPHON
       This page is part of release 4.10 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				  2017-03-13				FTS(3)