NAME
fts,
fts_open,
fts_read,
fts_children,
fts_set,
fts_close —
traverse a file
hierarchy
LIBRARY
Standard C Library (libc, -lc)
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, 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”
(ignoring symbolic links) or physically (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 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_W
- A whiteout object.
-
-
- 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
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_WHITEOUT
- Return whiteout entries, which are normally hidden.
-
-
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 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
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.
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
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
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),
symlink(7)
STANDARDS
The
fts utility was expected to be included in the
IEEE Std 1003.1-1988 (“POSIX.1”) revision.
But twenty years later, it still was not included in the
IEEE
Std 1003.1-2008 (“POSIX.1”) revision.