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


Committed.

MT-LEVEL
See Locking.

SEE ALSO


find(1), chdir(2), stat(2), qsort(3C), attributes(7)

illumos March 28, 2017 illumos