fts

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
       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).

       ┌───────────────────────────────────┬───────────────┬───────────┐
       │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 5.07 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                             2020-04-11                            FTS(3)