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NAME

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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fts.h>

       FTS *fts_open(char *const *path_argv, int options,
                     int (*_Nullable 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;    /* [l]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 [l]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 [l]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 [l]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_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:  the  fts_statp  field  is  obtained  via
              stat(2) with a fallback to lstat(2).

       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: the fts_statp field is obtained via lstat(2).

       FTS_COMFOLLOW
              This option causes any symbolic link specified  as  a  root  path  to  be  followed
              immediately, as if via FTS_LOGICAL, regardless of the primary mode.

       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.  This 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 fts_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 fts_statp field undefined.

       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
       errno  to  0.  If an error unrelated to a file in the hierarchy occurs, fts_read() returns
       NULL and sets errno to indicate the error.  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 to indicate the error.

       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).

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

       ENOENT Any element of path_argv was an empty string.

       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 [l]stat(2).

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

       EINVAL options or instr was invalid.

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 │
       └─────────────────────────────────────────────────────────────┴───────────────┴───────────┘

STANDARDS

       None.

HISTORY

       glibc 2.  4.4BSD.

BUGS

       Before glibc 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), lstat(2), stat(2), ftw(3), qsort(3)