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.Dd March 28, 2017
.Dt FTS 3C
.Os
.Sh NAME
.Nm fts_open ,
.Nm fts_read ,
.Nm fts_children ,
.Nm fts_set ,
.Nm fts_close
.Nd traverse a file hierarchy
.Sh SYNOPSIS
.In sys/types.h
.In sys/stat.h
.In fts.h
.Ft FTS *
.Fo fts_open
.Fa "char * const *path_argv"
.Fa "int options"
.Fa "int (*compar)(const FTSENT **, const FTSENT **)"
.Fc
.Ft FTSENT *
.Fn fts_read "FTS *ftsp"
.Ft FTSENT *
.Fn fts_children "FTS *ftsp" "int options"
.Ft int
.Fn fts_set "FTS *ftsp" "FTSENT *f" "int option"
.Ft int
.Fn fts_close "FTS *ftsp"
.Sh DESCRIPTION
The
.Nm fts
functions are provided for traversing
.Ux
file hierarchies.
The
.Fn fts_open
function returns a
.Dq handle
on a file hierarchy, which is then supplied to
the other
.Nm fts
functions.
The function
.Fn fts_read
returns a pointer to a structure describing one of the files in the file
hierarchy.
The function
.Fn 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.
.Pp
In general, directories are visited two distinguishable times; in pre-order
.Pq before any of their descendants are visited
and in post-order
.Pq after all of their descendants have been visited .
Files are visited once.
It is possible to walk the hierarchy
.Dq logically
.Pq following symbolic links
or
.Dq physically
.Pq not following symbolic links ,
order the walk of the hierarchy, or
prune and/or re-visit portions of the hierarchy.
.Pp
Two structures are defined
.Pq and typedef'd
in the include file
.In fts.h .
The first is
.Dv FTS ,
the structure that represents the file hierarchy itself.
The second is
.Li FTSENT ,
the structure that represents a file in the file
hierarchy.
Normally, an
.Li FTSENT
structure is returned for every file in the file
hierarchy.
In this manual page,
.Dq file
and
.Dq Li FTSENT No structure
are generally
interchangeable.
.Pp
The
.Li FTSENT
structure contains at least the following fields, which are
described in greater detail below:
.Bd -literal
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;
.Ed
.Pp
These fields are defined as follows:
.Bl -tag -width "fts_namelen"
.It Fa fts_info
One of the following flags describing the returned
.Li FTSENT
structure and
the file it represents.
With the exception of directories without errors
.Pq Dv FTS_D ,
all of these
entries are terminal, that is, they will not be revisited, nor will any
of their descendants be visited.
.Bl -tag -width FTS_DEFAULT
.It Dv FTS_D
A directory being visited in pre-order.
.It Dv FTS_DC
A directory that causes a cycle in the tree.
.Po The
.Fa fts_cycle
field of the
.Li FTSENT
structure will be filled in as well.
.Pc
.It Dv FTS_DEFAULT
Any
.Li FTSENT
structure that represents a file type not explicitly described
by one of the other
.Fa fts_info
values.
.It Dv FTS_DNR
A directory which cannot be read.
This is an error return, and the
.Fa fts_errno
field will be set to indicate what caused the error.
.It Dv FTS_DOT
A file named
.Dq \&.
or
.Dq ..
which was not specified as a file name to
.Fn fts_open
.Pq see Dv FTS_SEEDOT .
.It Dv FTS_DP
A directory being visited in post-order.
The contents of the
.Li FTSENT
structure will be unchanged from when
it was returned in pre-order, i.e., with the
.Fa fts_info
field set to
.Dv FTS_D .
.It Dv FTS_ERR
This is an error return, and the
.Fa fts_errno
field will be set to indicate what caused the error.
.It Dv FTS_F
A regular file.
.It Dv FTS_NS
A file for which no
.Xr stat 2
information was available.
The contents of the
.Fa fts_statp
field are undefined.
This is an error return, and the
.Fa fts_errno
field will be set to indicate what caused the error.
.It Dv FTS_NSOK
A file for which no
.Xr stat 2
information was requested.
The contents of the
.Fa fts_statp
field are undefined.
.It Dv FTS_SL
A symbolic link.
.It Dv FTS_SLNONE
A symbolic link with a non-existent target.
The contents of the
.Fa fts_statp
field reference the file characteristic information for the symbolic link
itself.
.El
.It Fa fts_accpath
A path for accessing the file from the current directory.
.It Fa fts_path
The path for the file relative to the root of the traversal.
This path contains the path specified to
.Fn fts_open
as a prefix.
.It Fa fts_pathlen
The length of the string referenced by
.Fa fts_path .
.It Fa fts_name
The name of the file.
.It Fa fts_namelen
The length of the string referenced by
.Fa fts_name .
.It Fa fts_level
The depth of the traversal, numbered from \-1 to N, where this file
was found.
The
.Li FTSENT
structure representing the parent of the starting point
.Pq or root
of the traversal is numbered
.Dv FTS_ROOTPARENTLEVEL
.Pq \-1 ,
and the
.Li FTSENT
structure for the root
itself is numbered
.Dv FTS_ROOTLEVEL
.Pq 0 .
Note that while
.Fa fts_level
cannot hold a number of levels greater than
.Dv FTS_MAXLEVEL ,
the
.Nm fts
functions themselves are not limited to a fixed number
of levels.
Application code that inspects
.Fa fts_level
should be written with this in mind.
.It Fa fts_errno
Upon return of an
.Li FTSENT
structure from the
.Fn fts_children
or
.Fn fts_read
functions, with its
.Fa fts_info
field set to
.Dv FTS_DNR ,
.Dv FTS_ERR
or
.Dv FTS_NS ,
the
.Fa fts_errno
field contains the value of the external variable
.Va errno
specifying the cause of the error.
Otherwise, the contents of the
.Fa fts_errno
field are undefined.
.It Fa fts_number
This field is provided for the use of the application program and is
not modified by the
.Nm fts
functions.
It is initialized to 0.
.It Fa fts_pointer
This field is provided for the use of the application program and is
not modified by the
.Nm fts
functions.
It is initialized to
.Dv NULL .
.It Fa fts_parent
A pointer to the
.Li 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
.Fa fts_level ,
.Fa fts_number
and
.Fa fts_pointer
fields are guaranteed to be initialized.
.It Fa fts_link
Upon return from the
.Fn fts_children
function, the
.Fa fts_link
field points to the next structure in the null-terminated
linked list of directory members.
Otherwise, the contents of the
.Fa fts_link
field are undefined.
.It Fa fts_cycle
If a directory causes a cycle in the hierarchy
.Pq see Dv FTS_DC ,
either because of a hard link between two directories, or a symbolic link
pointing to a directory, the
.Fa fts_cycle
field of the structure will point to the
.Li FTSENT
structure in the hierarchy that references the same file as the current
.Li FTSENT
structure.
Otherwise, the contents of the
.Fa fts_cycle
field are undefined.
.It Fa fts_statp
A pointer to
.Xr stat 2
information for the file.
.El
.Pp
A single buffer is used for all of the paths of all of the files in the
file hierarchy.
Therefore, the
.Fa fts_path
and
.Fa fts_accpath
fields are guaranteed to be NUL terminated
.Em only
for the file most recently returned by
.Fn fts_read .
To use these fields to reference any files represented by other
.Li FTSENT
structures will require that the path buffer be modified using the
information contained in that
.Li FTSENT
structure's
.Fa fts_pathlen
field.
Any such modifications should be undone before further calls to
.Fn fts_read
are attempted.
The
.Fa fts_name
field is always NUL terminated.
.Ss FTS_OPEN
The
.Fn 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.
.Pp
There are
a number of options, at least one of which
.Po either
.Dv FTS_LOGICAL
or
.Dv FTS_PHYSICAL
.Pc
must be specified.
The
.Fa options
are selected by
.Tn OR Ns 'ing
the following values:
.Bl -tag -width "FTS_COMFOLLOW"
.It Dv FTS_COMFOLLOW
This option causes any symbolic link specified as a root path to be
followed immediately whether or not
.Dv FTS_LOGICAL
is also specified.
.It Dv FTS_LOGICAL
This option causes the
.Nm fts
routines to return
.Li 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
.Li FTSENT
structures
are returned to the application are those referencing non-existent files.
Either
.Dv FTS_LOGICAL
or
.Dv FTS_PHYSICAL
.Em must
be provided to the
.Fn fts_open
function.
.It Dv FTS_NOCHDIR
As a performance optimization, the
.Nm 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
.Dv FTS_NOCHDIR
option turns off this optimization, and the
.Nm fts
functions will not change the current directory.
Note that applications should not themselves change their current directory
and try to access files unless
.Dv FTS_NOCHDIR
is specified and absolute
pathnames were provided as arguments to
.Fn fts_open .
.It Dv FTS_NOSTAT
By default, returned
.Li FTSENT
structures reference file characteristic information
.Po the
.Fa statp
field
.Pc
for each file visited.
This option relaxes that requirement as a performance optimization,
allowing the
.Nm fts
functions to set the
.Fa fts_info
field to
.Dv FTS_NSOK
and leave the contents of the
.Fa statp
field undefined.
.It Dv FTS_PHYSICAL
This option causes the
.Nm fts
routines to return
.Li FTSENT
structures for symbolic links themselves instead
of the target files they point to.
If this option is set,
.Li FTSENT
structures for all symbolic links in the
hierarchy are returned to the application.
Either
.Dv FTS_LOGICAL
or
.Dv FTS_PHYSICAL
.Em must
be provided to the
.Fn fts_open
function.
.It Dv FTS_SEEDOT
By default, unless they are specified as path arguments to
.Fn fts_open ,
any files named
.Dq \&.
or
.Dq ..
encountered in the file hierarchy are ignored.
This option causes the
.Nm fts
routines to return
.Li FTSENT
structures for them.
.It Dv FTS_XDEV
This option prevents
.Nm fts
from descending into directories that have a different device number
than the file from which the descent began.
.El
.Pp
The
.Fa 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
.Li 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
.Fa fts_accpath ,
.Fa fts_path
and
.Fa fts_pathlen
fields of the
.Li FTSENT
structures may
.Em never
be used in this comparison.
If the
.Fa fts_info
field is set to
.Dv FTS_NS
or
.Dv FTS_NSOK ,
the
.Fa fts_statp
field may not either.
If the
.Fa compar
argument is
.Dv NULL ,
the directory traversal order is in the order listed in
.Fa path_argv
for the root paths, and in the order listed in the directory for
everything else.
.Pp
If an error occurs,
.Fn fts_open
returns
.Dv NULL
and sets
.Va errno
appropriately.
.Ss FTS_READ
The
.Fn fts_read
function returns a pointer to an
.Li FTSENT
structure describing a file in
the hierarchy.
Directories
.Pq 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.
.Po 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.
.Pc
.Pp
If all the members of the hierarchy have been returned,
.Fn fts_read
returns
.Dv NULL
and sets the external variable
.Va errno
to 0.
If an error unrelated to a file in the hierarchy occurs,
.Fn fts_read
returns
.Dv NULL
and sets
.Va errno
appropriately.
If an error related to a returned file occurs, a pointer to an
.Li FTSENT
structure is returned, and
.Va errno
may or may not have been set
.Pq see Fa fts_info .
.Pp
The
.Li FTSENT
structures returned by
.Fn fts_read
may be overwritten after a call to
.Fn fts_close
on the same file hierarchy stream or, after a call to
.Fn 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
.Fn fts_read
after the
.Li FTSENT
structure has been returned by the function
.Fn fts_read
in post-order.
.Ss FTS_CHILDREN
The
.Fn fts_children
function returns a pointer to an
.Li FTSENT
structure describing the first entry in a null-terminated
linked list of
the files in the directory represented by the
.Li FTSENT
structure most recently returned by
.Fn fts_read .
The list is linked through the
.Fa fts_link
field of the
.Li FTSENT
structure, and is ordered by the user-specified comparison function, if any.
Repeated calls to
.Fn fts_children
will recreate this linked list.
.Pp
As a special case, if
.Fn fts_read
has not yet been called for a hierarchy,
.Fn fts_children
will return a pointer to the files in the logical directory specified to
.Fn fts_open ,
i.e., the arguments specified to
.Fn fts_open .
Otherwise, if the
.Li FTSENT
structure most recently returned by
.Fn fts_read
is not a directory being visited in pre-order,
or the directory does not contain any files,
.Fn fts_children
returns
.Dv NULL
and sets
.Va errno
to 0.
If an error occurs,
.Fn fts_children
returns
.Dv NULL
and sets
.Va errno
appropriately.
.Pp
The
.Li FTSENT
structures returned by
.Fn fts_children
may be overwritten after a call to
.Fn fts_children ,
.Fn fts_close
or
.Fn fts_read
on the same file hierarchy stream.
.Pp
.Fa options
may be set to the following value:
.Bl -tag -width FTS_NAMEONLY
.It Dv 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
.Fa fts_name
and
.Fa fts_namelen
fields.
.El
.Ss FTS_SET
The function
.Fn fts_set
allows the user application to determine further processing for the file
.Fa f
of the stream
.Fa ftsp .
The
.Fn fts_set
function returns 0 on success or \-1 if an error occurred.
.Fa option
must be set to one of the following values:
.Bl -tag -width FTS_PHYSICAL
.It Dv FTS_AGAIN
Re-visit the file; any file type may be re-visited.
The next call to
.Fn fts_read
will return the referenced file.
The
.Fa fts_stat
and
.Fa 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
.Fn fts_read .
Normal use is for post-order directory visits, where it causes the
directory to be re-visited
.Pq in both pre and post-order
as well as all of its descendants.
.It Dv FTS_FOLLOW
The referenced file must be a symbolic link.
If the referenced file is the one most recently returned by
.Fn fts_read ,
the next call to
.Fn fts_read
returns the file with the
.Fa fts_info
and
.Fa 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
.Fn fts_children ,
the
.Fa fts_info
and
.Fa fts_statp
fields of the structure, when returned by
.Fn 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
.Fa fts_info
field will be set to
.Dv FTS_SLNONE .
.Pp
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.
.It Dv FTS_SKIP
No descendants of this file are visited.
The file may be one of those most recently returned by either
.Fn fts_children
or
.Fn fts_read .
.El
.Ss FTS_CLOSE
The
.Fn fts_close
function closes a file hierarchy stream
.Fa ftsp
and restores the current directory to the directory from which
.Fn fts_open
was called to open
.Fa ftsp .
.Rv -std fts_close
.Ss Locking
The fts routines provide no locking.
While the
.Fn fts_open
function is
.Sy Safe
and can be called from multiple threads simultaneously, the individual
handles returned from the
.Fn fts_open
function are not thread-safe.
If callers need to operate on a single
.Vt 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
.Fn fts_read ,
.Fn fts_children ,
.Fn fts_set ,
and
.Fn fts_close
functions are
.Sy Unsafe .
.Pp
These routines are not
.Sy Async-Signal-Safe
and callers should not assume that the implementation of these functions
will be
.Sy 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
.Xr pthread_atfork 3C .
.Sh ERRORS
The function
.Fn fts_open
may fail and set
.Va errno
for any of the errors specified for the library functions
.Xr open 2
and
.Xr malloc 3C .
.Pp
The function
.Fn fts_close
may fail and set
.Va errno
for any of the errors specified for the library function
.Xr fchdir 2 .
.Pp
The functions
.Fn fts_read
and
.Fn fts_children
may fail and set
.Va errno
for any of the errors specified for the library functions
.Xr chdir 2 ,
.Xr malloc 3C ,
.Xr opendir 3C ,
.Xr readdir 3C
and
.Xr stat 2 .
.Pp
In addition,
.Fn fts_children ,
.Fn fts_open
and
.Fn fts_set
may fail and set
.Va errno
as follows:
.Bl -tag -width Er
.It Er EINVAL
A specified option is invalid or
.Fa path_argv
is empty.
.El
.Sh INTERFACE STABILITY
.Sy Committed .
.Sh MT-LEVEL
See
.Sx Locking .
.Sh SEE ALSO
.Xr find 1 ,
.Xr chdir 2 ,
.Xr stat 2 ,
.Xr qsort 3C ,
.Xr attributes 7