FTS(3) Library Routines FTS(3)
NAME
fts - 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 (*com
par)(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, di‐
rectories 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 hierar‐
chy 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 it‐
self. The second is FTSENT, the structure that represents a file in
the file hierarchy. Normally, an FTSENT structure is returned for ev‐
ery file in the file hierarchy. In this manual page, ``file'' and
struct FTSENT are generally interchangeable. The FTSENT structure con‐
tains at least the following fields, which are described in greater de‐
tail 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 values describing the returned FT
SENT structure and the file it represents. With the ex‐
ception of directories without errors (FTS_D), all of
these entries are terminal, that is, they will not be re‐
visited, 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 er‐
ror 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 con‐
tents 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 avail‐
able. The contents of the fts_statp field are un‐
defined. This is an error return, and the fts_er
rno field will be set to indicate what caused the
error.
FTS_NSOK
A file for which no stat(2) information was re‐
quested. 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 traver‐
sal. 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 traver‐
sal 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 con‐
tents 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 direc‐
tories, 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 re‐
turned by fts_read. To use these fields to reference any files repre‐
sented 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 fur‐
ther 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_LOGI
CAL 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_LOGI
CAL 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-ex‐
istent 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 pro‐
vided 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, FT
SENT 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 af‐
ter, 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 directo‐
ries more than twice.)
If all the members of the hierarchy have been returned, fts_read re‐
turns NULL and sets the external variable errno to 0. If an error un‐
related to a file in the hierarchy occurs, fts_read returns NULL and
sets errno appropriately. If an error related to a returned file oc‐
curs, 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 un‐
til after a call to fts_read after the FTSENT structure has been re‐
turned by the function fts_read in post-order.
FTS_CHILDREN
The fts_children function returns a pointer to an FTSENT structure de‐
scribing the first entry in a NULL-terminated linked list of the files
in the directory represented by the FTSENT structure most recently re‐
turned 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 ap‐
propriately.
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 hierar‐
chy 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 re‐
turns 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 di‐
rectory 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 ref‐
erenced 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 re‐
flect the target of the symbolic link instead of the sym‐
bolic link itself. If the file is one of those most re‐
cently 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_chil
dren 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)
STANDARDS
The fts utility is expected to be included in a future POSIX 1003.1-88
revision.
GNO 22 January 1997 FTS(3)
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