Tribblix: manual page: fts.3c

FTS(3C) Standard C Library Functions FTS(3C)

NAME

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 option);

int
fts_close(FTS *ftsp);

DESCRIPTION

The fts functions are provided for traversing UNIX file hierarchies.
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 within the hierarchy.

In general, directories 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" (following
symbolic links) or "physically" (not following 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 {
unsigned short fts_info; /* flags for FTSENT structure */
char *fts_accpath; /* access path */
char *fts_path; /* root path */
size_t fts_pathlen; /* strlen(fts_path) */
char *fts_name; /* file name */
size_t fts_namelen; /* strlen(fts_name) */
int 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
specified 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 FTS_ROOTPARENTLEVEL (-1), and the
FTSENT structure for the root itself is numbered
FTS_ROOTLEVEL (0). Note that while fts_level cannot hold
a number of levels greater than FTS_MAXLEVEL, the fts
functions themselves are not limited to a fixed number of
levels. Application code that inspects fts_level should
be written with this in mind.

fts_errno Upon return of an 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
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, i.e.,
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 NUL 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 NUL 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
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 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 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 compar argument 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.

If an error occurs, fts_open() returns NULL and sets errno
appropriately.

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 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
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 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 directory 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 0. 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.

options 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 or -1 if an error occurred. 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
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 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 the value 0 if successful; otherwise
the value -1 is returned and the global variable errno is set to
indicate the error.

Locking

The fts routines provide no locking. While the fts_open() function is
Safe and can be called from multiple threads simultaneously, the
individual handles returned from the fts_open() function are not
thread-safe. If callers need to operate on a single FTS structure,
then it is their responsibility to ensure that none of the other
functions are called from multiple threads simultaneously. This
implies that the fts_read(), fts_children(), fts_set(), and fts_close()
functions are Unsafe.

These routines are not Async-Signal-Safe and callers should not assume
that the implementation of these functions will be Fork-Safe. If
callers implement their own locking structures around the use of these
routines, they must ensure that those locks are accounted for when
forking by the use of routines such as pthread_atfork(3C).

ERRORS

The function fts_open() may fail and set errno for any of the errors
specified for the library functions open(2) and malloc(3C).

The function fts_close() may fail and set errno for any of the errors
specified for the library function fchdir(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(3C), opendir(3C), readdir(3C) and stat(2).

In addition, fts_children(), fts_open() and fts_set() may fail and set
errno as follows:

EINVAL A specified option is invalid or path_argv is empty.

INTERFACE STABILITY