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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).
┌────────────────────────────────────┬───────────────┬───────────┐
│ 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 5.10 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)