NAME | SYNOPSIS | DESCRIPTION | ERRORS | VERSIONS | CONFORMING TO | SEE ALSO | COLOPHON
FTS(3) Linux Programmer's Manual FTS(3)
fts, fts_open, fts_read, fts_children, fts_set, fts_close - traverse a file
hierarchy
#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);
The fts functions are provided for traversing 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 {
unsigned 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; /* filename */
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 filename 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, that is, 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 nonexistent 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 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, that is, 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 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.
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 oring 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 nonexistent 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 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.
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.
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(), that is, 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.
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().
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.
The function fts_open() may fail and set errno for any of the errors specified
for open(2) and malloc(3).
The function fts_close() may fail and set errno for any of the errors
specified for chdir(2) and close(2).
The functions fts_read() and fts_children() may fail and set errno for any of
the errors specified for 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.
These functions are available in Linux since glibc2.
4.4BSD.
find(1), chdir(2), stat(2), ftw(3), qsort(3)
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2007-12-28 FTS(3)