FTS(3) Linux Programmer's Manual FTS(3)NAME
fts, 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 instr);
int fts_set(FTS *ftsp, FTSENT *f, int instr);
int fts_close(FTS *ftsp);
DESCRIPTION
The fts functions are provided for traversing file hierarchies. A sim‐
ple overview is that the fts_open() function returns a "handle" (of
type FTS *) that refers to a file hierarchy "stream". This handle 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 postorder
(after all of their descendants have been visited). Files are visited
once. It is possible to walk the hierarchy "logically" (visiting the
files that symbolic links point to) or physically (visiting the sym‐
bolic links themselves), order the walk of the hierarchy or prune
and/or revisit portions of the hierarchy.
Two structures (and associated types) are defined in the include file
<fts.h>. The first type is FTS, the structure that represents the file
hierarchy itself. The second type is FTSENT, the structure that repre‐
sents 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 fields describing a file. The structure
contains at least the following fields (there are additional fields
that should be considered private to the implementation):
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 values 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 preorder.
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 speci‐
fied as a filename to fts_open() (see FTS_SEE‐
DOT).
FTS_DP A directory being visited in postorder. 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 sym‐
bolic 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 traversal is
numbered -1, and the FTSENT structure for the root itself
is numbered 0.
fts_errno If fts_children() or fts_read() returns an FTSENT structure
whose fts_info field is set to FTS_DNR, FTS_ERR, or FTS_NS,
the fts_errno field contains the error number (i.e., the
errno value) 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 pro‐
gram and is not modified by the fts functions. It is ini‐
tialized to 0.
fts_pointer This field is provided for the use of the application pro‐
gram and is not modified by the fts functions. It is ini‐
tialized 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 directo‐
ries, 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 buf‐
fer be modified using the information contained in that FTSENT struc‐
ture'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.
fts_open()
The fts_open() function takes a pointer to an array of character point‐
ers 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
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_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 nonex‐
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,
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.
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 preorder and
once in postorder. 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 direc‐
tories 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 postorder.
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_chil‐
dren() will re-create this linked list.
As a special case, if fts_read() has not yet been called for a hierar‐
chy, 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 preorder, 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.
The instr argument is either zero or 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.
The instr argument is either 0 (meaning "do nothing") or one of the
following values:
FTS_AGAIN Revisit the file; any file type may be revisited. 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
postorder directory visits, where it causes the directory
to be revisited (in both preorder and postorder) 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
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 preorder
return, followed by the return of all of its descendants,
followed by a postorder 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 the file hierarchy stream referred to
by 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 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), read‐
dir(3), and stat(2).
In addition, fts_children(), fts_open(), and fts_set() may fail and set
errno as follows:
EINVAL options or instr was invalid.
VERSIONS
These functions are available in Linux since glibc2.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────────────────┬───────────────┬───────────┐
│Interface │ Attribute │ Value │
├───────────────────────────────────┼───────────────┼───────────┤
│fts_open(), fts_set(), fts_close() │ Thread safety │ MT-Safe │
├───────────────────────────────────┼───────────────┼───────────┤
│fts_read(), fts_children() │ Thread safety │ MT-Unsafe │
└───────────────────────────────────┴───────────────┴───────────┘
CONFORMING TO
4.4BSD.
BUGS
In versions of glibc before 2.23, all of the APIs described in this man
page are not safe when compiling a program using the LFS APIs (e.g.,
when compiling with -D_FILE_OFFSET_BITS=64).
SEE ALSOfind(1), chdir(2), stat(2), ftw(3), qsort(3)COLOPHON
This page is part of release 4.14 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 FTS(3)
