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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 simple 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 preorder (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 symbolic
       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 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 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) +
                                                strlen(fts_name) */
               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 specified as a filename
                               to fts_open() (see FTS_SEEDOT).

                   FTS_DP      A directory being visited  in  postorder.   The  contents  of  the
                               FTSENT  structure  will  be unchanged from when it was returned in
                               preorder, 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 symbolic 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 traversal.  This path
                   contains the path specified to fts_open() as a prefix.

       fts_pathlen The sum of the lengths of the strings referenced by fts_path and fts_name.

       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  program  and  is  not
                   modified 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
                   modified by the fts functions.  It is initialized 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  directories,  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 buffer be modified
       using the information contained in that FTSENT structure'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 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 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_LOGICAL 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 nonexistent 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 provided  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 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 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_children() will re-create 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(),  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 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 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_children() 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), readdir(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).

       ┌───────────────────────────────────┬───────────────┬───────────┐
       │InterfaceAttributeValue     │
       ├───────────────────────────────────┼───────────────┼───────────┤
       │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 4.16 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/.