fts_read

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) +
                                                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 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  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  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 4.15 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                             2018-02-02                            FTS(3)
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