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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 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)