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) */
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 length of the string referenced by fts_path.
- 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 |
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 4.10 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/.