fts_read
FTS(3) BSD Library Functions 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 options);
int
fts_set(FTS *ftsp, FTSENT *f, int options);
int
fts_close(FTS *ftsp);
DESCRIPTION
The fts functions are provided for traversing UNIX file hierarchies. A
simple overview is that the fts_open() function returns a ``handle'' on a
file hierarchy, which 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, direc-
tories are visited two distinguishable times; in pre-order (before any of
their descendants are visited) and in post-order (after all of their
descendants have been visited). Files are visited once. It is possible
to walk the hierarchy ``logically'' (ignoring symbolic links) or physi-
cally (visiting symbolic links), order the walk of the hierarchy or prune
and/or re-visit portions of the hierarchy.
Two structures are defined (and typedef'd) in the include file <fts.h>.
The first is FTS, the structure that represents the file hierarchy
itself. The second 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
at least the following fields, which are described in greater detail
below:
typedef struct _ftsent {
u_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; /* file name */
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 flags 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 pre-order.
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 speci-
fied as a file name to fts_open() (see
FTS_SEEDOT).
FTS_DP A directory being visited in post-order. The
contents of the FTSENT structure will be
unchanged from when it was returned in pre-
order, i.e. 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 non-existent 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 Upon return of a FTSENT structure from the fts_children() or
fts_read() functions, with its fts_info field set to
FTS_DNR, FTS_ERR or FTS_NS, the fts_errno field contains the
value of the external variable errno 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 pro-
gram and is not modified by the fts functions. It is ini-
tialized to 0.
fts_pointer This field is provided for the use of the application pro-
gram and is not modified by the fts functions. It is ini-
tialized to NULL.
fts_parent A pointer to the FTSENT structure referencing the file in
the hierarchy immediately above the current file, i.e. the
directory of which this file is a member. A parent struc-
ture for the initial entry point is provided as well, how-
ever, 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 guar-
anteed 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 or'ing
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 struc-
tures for the targets of symbolic links instead of the sym-
bolic links themselves. If this option is set, the only
symbolic links for which FTSENT structures are returned to
the application are those referencing non-existent 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 applica-
tions 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 char-
acteristic information (the statp field) for each file vis-
ited. This option relaxes that requirement as a perfor-
mance 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 struc-
tures for symbolic links themselves instead of the target
files they point to. If this option is set, FTSENT struc-
tures 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 point-
ers 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 describ-
ing a file in the hierarchy. Directories (that are readable and do not
cause cycles) are visited at least twice, once in pre-order and once in
post-order. All other files are visited at least once. (Hard links
between directories that do not cause cycles or symbolic links to sym-
bolic 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 post-order.
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 recreate 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 direc-
tory specified to fts_open(), i.e. the arguments specified to fts_open().
Otherwise, if the FTSENT structure most recently returned by fts_read()
is not a directory being visited in pre-order, 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 appropri-
ately.
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.
Option may be set to 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. Option must be set to
one of the following values:
FTS_AGAIN Re-visit the file; any file type may be re-visited. 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
post-order directory visits, where it causes the directory
to be re-visited (in both pre and post-order) as well as
all of its descendants.
FTS_FOLLOW The referenced file must be a symbolic link. If the refer-
enced 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 pre-order
return, followed by the return of all of its descendants,
followed by a post-order 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 a file hierarchy stream 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 the library functions open(2) and malloc(3).
The function fts_close() may fail and set errno for any of the errors
specified for the library functions chdir(2) and close(2).
The functions fts_read() and fts_children() may fail and set errno for
any of the errors specified for the library functions 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] The options were invalid.
SEE ALSO
find(1), chdir(2), stat(2), qsort(3)
CONFORMING TO
BSD 4.4. The fts utility is expected to be included in a future IEEE Std
1003.1-1988 (``POSIX.1'') revision.
AVAILABILITY
These functions are available in Linux since glibc2.
BSD April 16, 1994 BSD
