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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() re-
       turns 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 un-
                               changed 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 re-
                               quested.  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 re-
       turned by fts_read().  To use these fields to reference any files  rep-
       resented  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 fur-
       ther 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, FT-
                     SENT 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 af-
       ter, 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  de-
       scribing  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()  re-
       turns  NULL and sets the external variable errno to 0.  If an error un-
       related to a file in the hierarchy occurs, fts_read() returns NULL  and
       sets  errno  appropriately.  If an error related to a returned file oc-
       curs, 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  un-
       til  after a call to fts_read() after the FTSENT structure has been re-
       turned 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  re-
       cently 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  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  di-
       rectory  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 af-
       ter 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 re-
                    turn, 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 at-
       tributes(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 5.05 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)

NAME | SYNOPSIS | DESCRIPTION | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | BUGS | SEE ALSO | COLOPHON