fts(3) — Linux manual page

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FTS(3)                  Linux Programmer's Manual                 FTS(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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 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         top

       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         top

       These functions are available in Linux since glibc2.

ATTRIBUTES         top

       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         top

       4.4BSD.

BUGS         top

       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         top

       find(1), chdir(2), stat(2), ftw(3), qsort(3)

COLOPHON         top

       This page is part of release 5.11 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                          2021-03-22                         FTS(3)

Pages that refer to this page: ftw(3)