NAME¶
File::Temp - return name and handle of a temporary file safely
VERSION¶
version 0.2304
SYNOPSIS¶
use File::Temp qw/ tempfile tempdir /;
$fh = tempfile();
($fh, $filename) = tempfile();
($fh, $filename) = tempfile( $template, DIR => $dir);
($fh, $filename) = tempfile( $template, SUFFIX => '.dat');
($fh, $filename) = tempfile( $template, TMPDIR => 1 );
binmode( $fh, ":utf8" );
$dir = tempdir( CLEANUP => 1 );
($fh, $filename) = tempfile( DIR => $dir );
Object interface:
require File::Temp;
use File::Temp ();
use File::Temp qw/ :seekable /;
$fh = File::Temp->new();
$fname = $fh->filename;
$fh = File::Temp->new(TEMPLATE => $template);
$fname = $fh->filename;
$tmp = File::Temp->new( UNLINK => 0, SUFFIX => '.dat' );
print $tmp "Some data\n";
print "Filename is $tmp\n";
$tmp->seek( 0, SEEK_END );
The following interfaces are provided for compatibility with existing APIs. They
should not be used in new code.
MkTemp family:
use File::Temp qw/ :mktemp /;
($fh, $file) = mkstemp( "tmpfileXXXXX" );
($fh, $file) = mkstemps( "tmpfileXXXXXX", $suffix);
$tmpdir = mkdtemp( $template );
$unopened_file = mktemp( $template );
POSIX functions:
use File::Temp qw/ :POSIX /;
$file = tmpnam();
$fh = tmpfile();
($fh, $file) = tmpnam();
Compatibility functions:
$unopened_file = File::Temp::tempnam( $dir, $pfx );
DESCRIPTION¶
"File::Temp" can be used to create and open temporary files in a safe
way. There is both a function interface and an object-oriented interface. The
File::Temp constructor or the
tempfile() function can be used to return
the name and the open filehandle of a temporary file. The
tempdir()
function can be used to create a temporary directory.
The security aspect of temporary file creation is emphasized such that a
filehandle and filename are returned together. This helps guarantee that a
race condition can not occur where the temporary file is created by another
process between checking for the existence of the file and its opening.
Additional security levels are provided to check, for example, that the sticky
bit is set on world writable directories. See "safe_level" for more
information.
For compatibility with popular C library functions, Perl implementations of the
mkstemp() family of functions are provided. These are,
mkstemp(),
mkstemps(),
mkdtemp() and
mktemp().
Additionally, implementations of the standard POSIX
tmpnam() and
tmpfile() functions are provided if required.
Implementations of
mktemp(),
tmpnam(), and
tempnam() are
provided, but should be used with caution since they return only a filename
that was valid when function was called, so cannot guarantee that the file
will not exist by the time the caller opens the filename.
Filehandles returned by these functions support the seekable methods.
OBJECT-ORIENTED INTERFACE¶
This is the primary interface for interacting with "File::Temp". Using
the OO interface a temporary file can be created when the object is
constructed and the file can be removed when the object is no longer required.
Note that there is no method to obtain the filehandle from the
"File::Temp" object. The object itself acts as a filehandle. The
object isa "IO::Handle" and isa "IO::Seekable" so all
those methods are available.
Also, the object is configured such that it stringifies to the name of the
temporary file and so can be compared to a filename directly. It numifies to
the "refaddr" the same as other handles and so can be compared to
other handles with "==".
$fh eq $filename # as a string
$fh != \*STDOUT # as a number
- new
- Create a temporary file object.
my $tmp = File::Temp->new();
by default the object is constructed as if "tempfile" was called
without options, but with the additional behaviour that the temporary file
is removed by the object destructor if UNLINK is set to true (the
default).
Supported arguments are the same as for "tempfile": UNLINK
(defaulting to true), DIR, EXLOCK and SUFFIX. Additionally, the filename
template is specified using the TEMPLATE option. The OPEN option is not
supported (the file is always opened).
$tmp = File::Temp->new( TEMPLATE => 'tempXXXXX',
DIR => 'mydir',
SUFFIX => '.dat');
Arguments are case insensitive.
Can call croak() if an error occurs.
- newdir
- Create a temporary directory using an object oriented interface.
$dir = File::Temp->newdir();
By default the directory is deleted when the object goes out of scope.
Supports the same options as the "tempdir" function. Note that
directories created with this method default to CLEANUP => 1.
$dir = File::Temp->newdir( $template, %options );
A template may be specified either with a leading template or with a
TEMPLATE argument.
- filename
- Return the name of the temporary file associated with this object (if the
object was created using the "new" constructor).
$filename = $tmp->filename;
This method is called automatically when the object is used as a
string.
- dirname
- Return the name of the temporary directory associated with this object (if
the object was created using the "newdir" constructor).
$dirname = $tmpdir->dirname;
This method is called automatically when the object is used in string
context.
- unlink_on_destroy
- Control whether the file is unlinked when the object goes out of scope.
The file is removed if this value is true and $KEEP_ALL is not.
$fh->unlink_on_destroy( 1 );
Default is for the file to be removed.
- DESTROY
- When the object goes out of scope, the destructor is called. This
destructor will attempt to unlink the file (using unlink1) if the
constructor was called with UNLINK set to 1 (the default state if UNLINK
is not specified).
No error is given if the unlink fails.
If the object has been passed to a child process during a fork, the file
will be deleted when the object goes out of scope in the parent.
For a temporary directory object the directory will be removed unless the
CLEANUP argument was used in the constructor (and set to false) or
"unlink_on_destroy" was modified after creation. Note that if a
temp directory is your current directory, it cannot be removed - a warning
will be given in this case. "chdir()" out of the directory
before letting the object go out of scope.
If the global variable $KEEP_ALL is true, the file or directory will not be
removed.
FUNCTIONS¶
This section describes the recommended interface for generating temporary files
and directories.
- tempfile
- This is the basic function to generate temporary files. The behaviour of
the file can be changed using various options:
$fh = tempfile();
($fh, $filename) = tempfile();
Create a temporary file in the directory specified for temporary files, as
specified by the tmpdir() function in File::Spec.
($fh, $filename) = tempfile($template);
Create a temporary file in the current directory using the supplied
template. Trailing `X' characters are replaced with random letters to
generate the filename. At least four `X' characters must be present at the
end of the template.
($fh, $filename) = tempfile($template, SUFFIX => $suffix)
Same as previously, except that a suffix is added to the template after the
`X' translation. Useful for ensuring that a temporary filename has a
particular extension when needed by other applications. But see the
WARNING at the end.
($fh, $filename) = tempfile($template, DIR => $dir);
Translates the template as before except that a directory name is specified.
($fh, $filename) = tempfile($template, TMPDIR => 1);
Equivalent to specifying a DIR of "File::Spec->tmpdir", writing
the file into the same temporary directory as would be used if no template
was specified at all.
($fh, $filename) = tempfile($template, UNLINK => 1);
Return the filename and filehandle as before except that the file is
automatically removed when the program exits (dependent on $KEEP_ALL).
Default is for the file to be removed if a file handle is requested and to
be kept if the filename is requested. In a scalar context (where no
filename is returned) the file is always deleted either (depending on the
operating system) on exit or when it is closed (unless $KEEP_ALL is true
when the temp file is created).
Use the object-oriented interface if fine-grained control of when a file is
removed is required.
If the template is not specified, a template is always automatically
generated. This temporary file is placed in tmpdir() (File::Spec)
unless a directory is specified explicitly with the DIR option.
$fh = tempfile( DIR => $dir );
If called in scalar context, only the filehandle is returned and the file
will automatically be deleted when closed on operating systems that
support this (see the description of tmpfile() elsewhere in this
document). This is the preferred mode of operation, as if you only have a
filehandle, you can never create a race condition by fumbling with the
filename. On systems that can not unlink an open file or can not mark a
file as temporary when it is opened (for example, Windows NT uses the
"O_TEMPORARY" flag) the file is marked for deletion when the
program ends (equivalent to setting UNLINK to 1). The "UNLINK"
flag is ignored if present.
(undef, $filename) = tempfile($template, OPEN => 0);
This will return the filename based on the template but will not open this
file. Cannot be used in conjunction with UNLINK set to true. Default is to
always open the file to protect from possible race conditions. A warning
is issued if warnings are turned on. Consider using the tmpnam()
and mktemp() functions described elsewhere in this document if
opening the file is not required.
If the operating system supports it (for example BSD derived systems), the
filehandle will be opened with O_EXLOCK (open with exclusive file lock).
This can sometimes cause problems if the intention is to pass the filename
to another system that expects to take an exclusive lock itself (such as
DBD::SQLite) whilst ensuring that the tempfile is not reused. In this
situation the "EXLOCK" option can be passed to tempfile. By
default EXLOCK will be true (this retains compatibility with earlier
releases).
($fh, $filename) = tempfile($template, EXLOCK => 0);
Options can be combined as required.
Will croak() if there is an error.
- tempdir
- This is the recommended interface for creation of temporary directories.
By default the directory will not be removed on exit (that is, it won't be
temporary; this behaviour can not be changed because of issues with
backwards compatibility). To enable removal either use the CLEANUP option
which will trigger removal on program exit, or consider using the
"newdir" method in the object interface which will allow the
directory to be cleaned up when the object goes out of scope.
The behaviour of the function depends on the arguments:
$tempdir = tempdir();
Create a directory in tmpdir() (see File::Spec).
$tempdir = tempdir( $template );
Create a directory from the supplied template. This template is similar to
that described for tempfile(). `X' characters at the end of the
template are replaced with random letters to construct the directory name.
At least four `X' characters must be in the template.
$tempdir = tempdir ( DIR => $dir );
Specifies the directory to use for the temporary directory. The temporary
directory name is derived from an internal template.
$tempdir = tempdir ( $template, DIR => $dir );
Prepend the supplied directory name to the template. The template should not
include parent directory specifications itself. Any parent directory
specifications are removed from the template before prepending the
supplied directory.
$tempdir = tempdir ( $template, TMPDIR => 1 );
Using the supplied template, create the temporary directory in a standard
location for temporary files. Equivalent to doing
$tempdir = tempdir ( $template, DIR => File::Spec->tmpdir);
but shorter. Parent directory specifications are stripped from the template
itself. The "TMPDIR" option is ignored if "DIR" is set
explicitly. Additionally, "TMPDIR" is implied if neither a
template nor a directory are supplied.
$tempdir = tempdir( $template, CLEANUP => 1);
Create a temporary directory using the supplied template, but attempt to
remove it (and all files inside it) when the program exits. Note that an
attempt will be made to remove all files from the directory even if they
were not created by this module (otherwise why ask to clean it up?). The
directory removal is made with the rmtree() function from the
File::Path module. Of course, if the template is not specified, the
temporary directory will be created in tmpdir() and will also be
removed at program exit.
Will croak() if there is an error.
MKTEMP FUNCTIONS¶
The following functions are Perl implementations of the
mktemp() family
of temp file generation system calls.
- mkstemp
- Given a template, returns a filehandle to the temporary file and the name
of the file.
($fh, $name) = mkstemp( $template );
In scalar context, just the filehandle is returned.
The template may be any filename with some number of X's appended to it, for
example /tmp/temp.XXXX. The trailing X's are replaced with unique
alphanumeric combinations.
Will croak() if there is an error.
- mkstemps
- Similar to mkstemp(), except that an extra argument can be supplied
with a suffix to be appended to the template.
($fh, $name) = mkstemps( $template, $suffix );
For example a template of "testXXXXXX" and suffix of
".dat" would generate a file similar to testhGji_w.dat.
Returns just the filehandle alone when called in scalar context.
Will croak() if there is an error.
- mkdtemp
- Create a directory from a template. The template must end in X's that are
replaced by the routine.
$tmpdir_name = mkdtemp($template);
Returns the name of the temporary directory created.
Directory must be removed by the caller.
Will croak() if there is an error.
- mktemp
- Returns a valid temporary filename but does not guarantee that the file
will not be opened by someone else.
$unopened_file = mktemp($template);
Template is the same as that required by mkstemp().
Will croak() if there is an error.
POSIX FUNCTIONS¶
This section describes the re-implementation of the
tmpnam() and
tmpfile() functions described in POSIX using the
mkstemp() from
this module.
Unlike the POSIX implementations, the directory used for the temporary file is
not specified in a system include file ("P_tmpdir") but simply
depends on the choice of
tmpdir() returned by File::Spec. On some
implementations this location can be set using the "TMPDIR"
environment variable, which may not be secure. If this is a problem, simply
use
mkstemp() and specify a template.
- tmpnam
- When called in scalar context, returns the full name (including path) of a
temporary file (uses mktemp()). The only check is that the file
does not already exist, but there is no guarantee that that condition will
continue to apply.
$file = tmpnam();
When called in list context, a filehandle to the open file and a filename
are returned. This is achieved by calling mkstemp() after
constructing a suitable template.
($fh, $file) = tmpnam();
If possible, this form should be used to prevent possible race conditions.
See "tmpdir" in File::Spec for information on the choice of
temporary directory for a particular operating system.
Will croak() if there is an error.
- tmpfile
- Returns the filehandle of a temporary file.
$fh = tmpfile();
The file is removed when the filehandle is closed or when the program exits.
No access to the filename is provided.
If the temporary file can not be created undef is returned. Currently this
command will probably not work when the temporary directory is on an NFS
file system.
Will croak() if there is an error.
ADDITIONAL FUNCTIONS¶
These functions are provided for backwards compatibility with common tempfile
generation C library functions.
They are not exported and must be addressed using the full package name.
- tempnam
- Return the name of a temporary file in the specified directory using a
prefix. The file is guaranteed not to exist at the time the function was
called, but such guarantees are good for one clock tick only. Always use
the proper form of "sysopen" with "O_CREAT | O_EXCL"
if you must open such a filename.
$filename = File::Temp::tempnam( $dir, $prefix );
Equivalent to running mktemp() with $dir/$prefixXXXXXXXX (using unix
file convention as an example)
Because this function uses mktemp(), it can suffer from race
conditions.
Will croak() if there is an error.
UTILITY FUNCTIONS¶
Useful functions for dealing with the filehandle and filename.
- unlink0
- Given an open filehandle and the associated filename, make a safe unlink.
This is achieved by first checking that the filename and filehandle
initially point to the same file and that the number of links to the file
is 1 (all fields returned by stat() are compared). Then the
filename is unlinked and the filehandle checked once again to verify that
the number of links on that file is now 0. This is the closest you can
come to making sure that the filename unlinked was the same as the file
whose descriptor you hold.
unlink0($fh, $path)
or die "Error unlinking file $path safely";
Returns false on error but croaks() if there is a security anomaly.
The filehandle is not closed since on some occasions this is not required.
On some platforms, for example Windows NT, it is not possible to unlink an
open file (the file must be closed first). On those platforms, the actual
unlinking is deferred until the program ends and good status is returned.
A check is still performed to make sure that the filehandle and filename
are pointing to the same thing (but not at the time the end block is
executed since the deferred removal may not have access to the
filehandle).
Additionally, on Windows NT not all the fields returned by stat() can
be compared. For example, the "dev" and "rdev" fields
seem to be different. Also, it seems that the size of the file returned by
stat() does not always agree, with "stat(FH)" being more
accurate than "stat(filename)", presumably because of caching
issues even when using autoflush (this is usually overcome by waiting a
while after writing to the tempfile before attempting to
"unlink0" it).
Finally, on NFS file systems the link count of the file handle does not
always go to zero immediately after unlinking. Currently, this command is
expected to fail on NFS disks.
This function is disabled if the global variable $KEEP_ALL is true and an
unlink on open file is supported. If the unlink is to be deferred to the
END block, the file is still registered for removal.
This function should not be called if you are using the object oriented
interface since the it will interfere with the object destructor deleting
the file.
- cmpstat
- Compare "stat" of filehandle with "stat" of provided
filename. This can be used to check that the filename and filehandle
initially point to the same file and that the number of links to the file
is 1 (all fields returned by stat() are compared).
cmpstat($fh, $path)
or die "Error comparing handle with file";
Returns false if the stat information differs or if the link count is
greater than 1. Calls croak if there is a security anomaly.
On certain platforms, for example Windows, not all the fields returned by
stat() can be compared. For example, the "dev" and
"rdev" fields seem to be different in Windows. Also, it seems
that the size of the file returned by stat() does not always agree,
with "stat(FH)" being more accurate than
"stat(filename)", presumably because of caching issues even when
using autoflush (this is usually overcome by waiting a while after writing
to the tempfile before attempting to "unlink0" it).
Not exported by default.
- unlink1
- Similar to "unlink0" except after file comparison using cmpstat,
the filehandle is closed prior to attempting to unlink the file. This
allows the file to be removed without using an END block, but does mean
that the post-unlink comparison of the filehandle state provided by
"unlink0" is not available.
unlink1($fh, $path)
or die "Error closing and unlinking file";
Usually called from the object destructor when using the OO interface.
Not exported by default.
This function is disabled if the global variable $KEEP_ALL is true.
Can call croak() if there is a security anomaly during the
stat() comparison.
- cleanup
- Calling this function will cause any temp files or temp directories that
are registered for removal to be removed. This happens automatically when
the process exits but can be triggered manually if the caller is sure that
none of the temp files are required. This method can be registered as an
Apache callback.
Note that if a temp directory is your current directory, it cannot be
removed. "chdir()" out of the directory first before calling
"cleanup()". (For the cleanup at program exit when the CLEANUP
flag is set, this happens automatically.)
On OSes where temp files are automatically removed when the temp file is
closed, calling this function will have no effect other than to remove
temporary directories (which may include temporary files).
File::Temp::cleanup();
Not exported by default.
PACKAGE VARIABLES¶
These functions control the global state of the package.
- safe_level
- Controls the lengths to which the module will go to check the safety of
the temporary file or directory before proceeding. Options are:
- STANDARD
- Do the basic security measures to ensure the directory exists and is
writable, that temporary files are opened only if they do not already
exist, and that possible race conditions are avoided. Finally the unlink0
function is used to remove files safely.
- MEDIUM
- In addition to the STANDARD security, the output directory is checked to
make sure that it is owned either by root or the user running the program.
If the directory is writable by group or by other, it is then checked to
make sure that the sticky bit is set.
Will not work on platforms that do not support the "-k" test for
sticky bit.
- HIGH
- In addition to the MEDIUM security checks, also check for the possibility
of `` chown() giveaway'' using the POSIX sysconf() function.
If this is a possibility, each directory in the path is checked in turn
for safeness, recursively walking back to the root directory.
For platforms that do not support the POSIX "_PC_CHOWN_RESTRICTED"
symbol (for example, Windows NT) it is assumed that `` chown()
giveaway'' is possible and the recursive test is performed.
The level can be changed as follows:
File::Temp->safe_level( File::Temp::HIGH );
The level constants are not exported by the module.
Currently, you must be running at least perl v5.6.0 in order to run with MEDIUM
or HIGH security. This is simply because the safety tests use functions from
Fcntl that are not available in older versions of perl. The problem is that
the version number for Fcntl is the same in perl 5.6.0 and in 5.005_03 even
though they are different versions.
On systems that do not support the HIGH or MEDIUM safety levels (for example Win
NT or OS/2) any attempt to change the level will be ignored. The decision to
ignore rather than raise an exception allows portable programs to be written
with high security in mind for the systems that can support this without those
programs failing on systems where the extra tests are irrelevant.
If you really need to see whether the change has been accepted simply examine
the return value of "safe_level".
$newlevel = File::Temp->safe_level( File::Temp::HIGH );
die "Could not change to high security"
if $newlevel != File::Temp::HIGH;
- TopSystemUID
- This is the highest UID on the current system that refers to a root UID.
This is used to make sure that the temporary directory is owned by a
system UID ("root", "bin", "sys" etc) rather
than simply by root.
This is required since on many unix systems "/tmp" is not owned by
root.
Default is to assume that any UID less than or equal to 10 is a root UID.
File::Temp->top_system_uid(10);
my $topid = File::Temp->top_system_uid;
This value can be adjusted to reduce security checking if required. The
value is only relevant when "safe_level" is set to MEDIUM or
higher.
- $KEEP_ALL
- Controls whether temporary files and directories should be retained
regardless of any instructions in the program to remove them
automatically. This is useful for debugging but should not be used in
production code.
$File::Temp::KEEP_ALL = 1;
Default is for files to be removed as requested by the caller.
In some cases, files will only be retained if this variable is true when the
file is created. This means that you can not create a temporary file, set
this variable and expect the temp file to still be around when the program
exits.
- $DEBUG
- Controls whether debugging messages should be enabled.
$File::Temp::DEBUG = 1;
Default is for debugging mode to be disabled.
WARNING¶
For maximum security, endeavour always to avoid ever looking at, touching, or
even imputing the existence of the filename. You do not know that that
filename is connected to the same file as the handle you have, and attempts to
check this can only trigger more race conditions. It's far more secure to use
the filehandle alone and dispense with the filename altogether.
If you need to pass the handle to something that expects a filename then on a
unix system you can use ""/dev/fd/" . fileno($fh)" for
arbitrary programs. Perl code that uses the 2-argument version of
"open" can be passed ""+<=&" .
fileno($fh)". Otherwise you will need to pass the filename. You will have
to clear the close-on-exec bit on that file descriptor before passing it to
another process.
use Fcntl qw/F_SETFD F_GETFD/;
fcntl($tmpfh, F_SETFD, 0)
or die "Can't clear close-on-exec flag on temp fh: $!\n";
Temporary files and NFS¶
Some problems are associated with using temporary files that reside on NFS file
systems and it is recommended that a local filesystem is used whenever
possible. Some of the security tests will most probably fail when the temp
file is not local. Additionally, be aware that the performance of I/O
operations over NFS will not be as good as for a local disk.
Forking¶
In some cases files created by File::Temp are removed from within an END block.
Since END blocks are triggered when a child process exits (unless
"POSIX::_exit()" is used by the child) File::Temp takes care to only
remove those temp files created by a particular process ID. This means that a
child will not attempt to remove temp files created by the parent process.
If you are forking many processes in parallel that are all creating temporary
files, you may need to reset the random number seed using srand(EXPR) in each
child else all the children will attempt to walk through the same set of
random file names and may well cause themselves to give up if they exceed the
number of retry attempts.
Directory removal¶
Note that if you have chdir'ed into the temporary directory and it is
subsequently cleaned up (either in the END block or as part of object
destruction), then you will get a warning from
File::Path::rmtree().
Taint mode¶
If you need to run code under taint mode, updating to the latest File::Spec is
highly recommended.
BINMODE¶
The file returned by File::Temp will have been opened in binary mode if such a
mode is available. If that is not correct, use the "binmode()"
function to change the mode of the filehandle.
Note that you can modify the encoding of a file opened by File::Temp also by
using "binmode()".
HISTORY¶
Originally began life in May 1999 as an XS interface to the system
mkstemp() function. In March 2000, the OpenBSD
mkstemp() code
was translated to Perl for total control of the code's security checking, to
ensure the presence of the function regardless of operating system and to help
with portability. The module was shipped as a standard part of perl from
v5.6.1.
Thanks to Tom Christiansen for suggesting that this module should be written and
providing ideas for code improvements and security enhancements.
SEE ALSO¶
"tmpnam" in POSIX, "tmpfile" in POSIX, File::Spec,
File::Path
See IO::File and File::MkTemp, Apache::TempFile for different implementations of
temporary file handling.
See File::Tempdir for an alternative object-oriented wrapper for the
"tempdir" function.
# vim: ts=2 sts=2 sw=2 et:
SUPPORT¶
Bugs / Feature Requests¶
Please report any bugs or feature requests through the issue tracker at
<
http://rt.cpan.org/Public/Dist/Display.html?Name=File-Temp>. You will
be notified automatically of any progress on your issue.
Source Code¶
This is open source software. The code repository is available for public review
and contribution under the terms of the license.
<
https://github.com/Perl-Toolchain-Gang/File-Temp>
git clone https://github.com/Perl-Toolchain-Gang/File-Temp.git
AUTHOR¶
Tim Jenness <tjenness@cpan.org>
CONTRIBUTORS¶
- •
- Ben Tilly <btilly@gmail.com>
- •
- David Golden <dagolden@cpan.org>
- •
- David Steinbrunner <dsteinbrunner@pobox.com>
- •
- Ed Avis <eda@linux01.wcl.local>
- •
- James E. Keenan <jkeen@verizon.net>
- •
- Karen Etheridge <ether@cpan.org>
- •
- Kevin Ryde <user42@zip.com.au>
- •
- Olivier Mengue <dolmen@cpan.org>
- •
- Peter John Acklam <pjacklam@online.no>
- •
- Peter Rabbitson <ribasushi@cpan.org>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2013 by Tim Jenness and the UK Particle Physics
and Astronomy Research Council.
This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.