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.\" ========================================================================
.TH File::Temp 3 "2002-06-01" "perl v5.8.0" "Perl Programmers Reference Guide"
File::Temp \- return name and handle of a temporary file safely
\& use File::Temp qw/ tempfile tempdir /;
\& $dir = tempdir( CLEANUP => 1 );
\& ($fh, $filename) = tempfile( DIR => $dir );
\& ($fh, $filename) = tempfile( $template, DIR => $dir);
\& ($fh, $filename) = tempfile( $template, SUFFIX => '.dat');
\& use File::Temp qw/ :mktemp /;
\& ($fh, $file) = mkstemp( "tmpfileXXXXX" );
\& ($fh, $file) = mkstemps( "tmpfileXXXXXX", $suffix);
\& $tmpdir = mkdtemp( $template );
\& $unopened_file = mktemp( $template );
\&\s-1POSIX\s0 functions:
\& use File::Temp qw/ :POSIX /;
\& ($fh, $file) = tmpnam();
\& ($fh, $file) = tmpfile();
\& $unopened_file = File::Temp::tempnam( $dir, $pfx );
\&\f(CW\*(C`File::Temp\*(C'\fR can be used to create and open temporary files in a safe way.
The \fItempfile()\fR function can be used to return the name and the open
filehandle of a temporary file. The \fItempdir()\fR function can
be used to create a temporary directory.
The security aspect of temporary file creation is emphasized such that
a filehandle and filename are returned together. This helps guarantee
that a race condition can not occur where the temporary file is
created by another process between checking for the existence of the
file and its opening. Additional security levels are provided to
check, for example, that the sticky bit is set on world writable
directories. See \*(L"safe_level\*(R" for more information.
For compatibility with popular C library functions, Perl implementations of
the \fImkstemp()\fR family of functions are provided. These are, \fImkstemp()\fR,
\&\fImkstemps()\fR, \fImkdtemp()\fR and \fImktemp()\fR.
Additionally, implementations of the standard \s-1POSIX\s0
\&\fItmpnam()\fR and \fItmpfile()\fR functions are provided if required.
Implementations of \fImktemp()\fR, \fItmpnam()\fR, and \fItempnam()\fR are provided,
but should be used with caution since they return only a filename
that was valid when function was called, so cannot guarantee
that the file will not exist by the time the caller opens the filename.
This section describes the recommended interface for generating
temporary files and directories.
This is the basic function to generate temporary files.
The behaviour of the file can be changed using various options:
\& ($fh, $filename) = tempfile();
Create a temporary file in the directory specified for temporary
files, as specified by the \fItmpdir()\fR function in File::Spec.
\& ($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
\& ($fh, $filename) = tempfile($template, SUFFIX => $suffix)
Same as previously, except that a suffix is added to the template
after the `X' translation. Useful for ensuring that a temporary
filename has a particular extension when needed by other applications.
But see the \s-1WARNING\s0 at the end.
\& ($fh, $filename) = tempfile($template, DIR => $dir);
Translates the template as before except that a directory name
\& ($fh, $filename) = tempfile($template, UNLINK => 1);
Return the filename and filehandle as before except that the file is
automatically removed when the program exits. 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 on exit or when it is closed.
If the template is not specified, a template is always
automatically generated. This temporary file is placed in \fItmpdir()\fR
(File::Spec) unless a directory is specified explicitly with the
\& $fh = tempfile( $template, DIR => $dir );
If called in scalar context, only the filehandle is returned
and the file will automatically be deleted when closed (see
the description of \fItmpfile()\fR 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 \s-1NT\s0 uses the \f(CW\*(C`O_TEMPORARY\*(C'\fR flag))
the file is marked for deletion when the program ends (equivalent
to setting \s-1UNLINK\s0 to 1). The \f(CW\*(C`UNLINK\*(C'\fR 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
\&\s-1UNLINK\s0 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 \fItmpnam()\fR
and \fImktemp()\fR functions described elsewhere in this document
if opening the file is not required.
Options can be combined as required.
This is the recommended interface for creation of temporary directories.
The behaviour of the function depends on the arguments:
Create a directory in \fItmpdir()\fR (see File::Spec).
\& $tempdir = tempdir( $template );
Create a directory from the supplied template. This template is
similar to that described for \fItempfile()\fR. `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 \f(CW\*(C`TMPDIR\*(C'\fR option is ignored if \f(CW\*(C`DIR\*(C'\fR is set
explicitly. Additionally, \f(CW\*(C`TMPDIR\*(C'\fR is implied if neither a template
nor a directory are supplied.
\& $tempdir = tempdir( $template, CLEANUP => 1);
Create a temporary directory using the supplied template, but
attempt to remove it (and all files inside it) when the program
exits. Note that an attempt will be made to remove all files from
the directory even if they were not created by this module (otherwise
why ask to clean it up?). The directory removal is made with
the \fIrmtree()\fR function from the File::Path module.
Of course, if the template is not specified, the temporary directory
will be created in \fItmpdir()\fR and will also be removed at program exit.
.IX Header "MKTEMP FUNCTIONS"
The following functions are Perl implementations of the
\&\fImktemp()\fR family of temp file generation system calls.
Given a template, returns a filehandle to the temporary file and the name
\& ($fh, $name) = mkstemp( $template );
In scalar context, just the filehandle is returned.
The template may be any filename with some number of X's appended
to it, for example \fI/tmp/temp.XXXX\fR. The trailing X's are replaced
with unique alphanumeric combinations.
Similar to \fImkstemp()\fR, except that an extra argument can be supplied
with a suffix to be appended to the template.
\& ($fh, $name) = mkstemps( $template, $suffix );
For example a template of \f(CW\*(C`testXXXXXX\*(C'\fR and suffix of \f(CW\*(C`.dat\*(C'\fR
would generate a file similar to \fItesthGji_w.dat\fR.
Returns just the filehandle alone when called in scalar context.
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.
Returns undef on failure.
Directory must be removed by the caller.
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 \fImkstemp()\fR.
.IX Header "POSIX FUNCTIONS"
This section describes the re-implementation of the \fItmpnam()\fR
and \fItmpfile()\fR functions described in \s-1POSIX\s0
using the \fImkstemp()\fR from this module.
Unlike the \s-1POSIX\s0 implementations, the directory used
for the temporary file is not specified in a system include
file (\f(CW\*(C`P_tmpdir\*(C'\fR) but simply depends on the choice of \fItmpdir()\fR
returned by File::Spec. On some implementations this
location can be set using the \f(CW\*(C`TMPDIR\*(C'\fR environment variable, which
If this is a problem, simply use \fImkstemp()\fR and specify a template.
When called in scalar context, returns the full name (including path)
of a temporary file (uses \fImktemp()\fR). The only check is that the file does
not already exist, but there is no guarantee that that condition will
When called in list context, a filehandle to the open file and
a filename are returned. This is achieved by calling \fImkstemp()\fR
after constructing a suitable template.
\& ($fh, $file) = tmpnam();
If possible, this form should be used to prevent possible
See \*(L"tmpdir\*(R" in File::Spec for information on the choice of temporary
directory for a particular operating system.
In scalar context, returns the filehandle of a temporary file.
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 \s-1NFS\s0 file system.
.SH "ADDITIONAL FUNCTIONS"
.IX Header "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
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 \f(CW\*(C`sysopen\*(C'\fR
with \f(CW\*(C`O_CREAT | O_EXCL\*(C'\fR if you must open such a filename.
\& $filename = File::Temp::tempnam( $dir, $prefix );
Equivalent to running \fImktemp()\fR with \f(CW$dir\fR/$prefixXXXXXXXX
(using unix file convention as an example)
Because this function uses \fImktemp()\fR, it can suffer from race conditions.
.IX Header "UTILITY FUNCTIONS"
Useful functions for dealing with the filehandle and filename.
Given an open filehandle and the associated filename, make a safe
unlink. This is achieved by first checking that the filename and
filehandle initially point to the same file and that the number of
links to the file is 1 (all fields returned by \fIstat()\fR are compared).
Then the filename is unlinked and the filehandle checked once again to
verify that the number of links on that file is now 0. This is the
closest you can come to making sure that the filename unlinked was the
same as the file whose descriptor you hold.
\& unlink0($fh, $path) or die "Error unlinking file $path safely";
Returns false on error. The filehandle is not closed since on some
occasions this is not required.
On some platforms, for example Windows \s-1NT\s0, 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 \s-1NT\s0 not all the fields returned by \fIstat()\fR can
be compared. For example, the \f(CW\*(C`dev\*(C'\fR and \f(CW\*(C`rdev\*(C'\fR fields seem to be
different. Also, it seems that the size of the file returned by \fIstat()\fR
does not always agree, with \f(CW\*(C`stat(FH)\*(C'\fR being more accurate than
\&\f(CW\*(C`stat(filename)\*(C'\fR, 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 \f(CW\*(C`unlink0\*(C'\fR it).
Finally, on \s-1NFS\s0 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 \s-1NFS\s0 disks.
.IX Header "PACKAGE VARIABLES"
These functions control the global state of the package.
Controls the lengths to which the module will go to check the safety of the
temporary file or directory before proceeding.
Do the basic security measures to ensure the directory exists and
is writable, that the \fIumask()\fR is fixed before opening of the file,
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.
In addition to the \s-1STANDARD\s0 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 \f(CW\*(C`\-k\*(C'\fR test
In addition to the \s-1MEDIUM\s0 security checks, also check for the
possibility of ``\fIchown()\fR giveaway'' using the \s-1POSIX\s0
\&\fIsysconf()\fR function. If this is a possibility, each directory in the
path is checked in turn for safeness, recursively walking back to the
For platforms that do not support the \s-1POSIX\s0
\&\f(CW\*(C`_PC_CHOWN_RESTRICTED\*(C'\fR symbol (for example, Windows \s-1NT\s0) it is
assumed that ``\fIchown()\fR giveaway'' is possible and the recursive test
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 \s-1MEDIUM\s0 or \s-1HIGH\s0 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 \s-1HIGH\s0 or \s-1MEDIUM\s0 safety levels
(for example Win \s-1NT\s0 or \s-1OS/2\s0) 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 \f(CW\*(C`safe_level\*(C'\fR.
\& $newlevel = File::Temp->safe_level( File::Temp::HIGH );
\& die "Could not change to high security"
\& if $newlevel != File::Temp::HIGH;
This is the highest \s-1UID\s0 on the current system that refers to a root
\&\s-1UID\s0. This is used to make sure that the temporary directory is
owned by a system \s-1UID\s0 (\f(CW\*(C`root\*(C'\fR, \f(CW\*(C`bin\*(C'\fR, \f(CW\*(C`sys\*(C'\fR etc) rather than
This is required since on many unix systems \f(CW\*(C`/tmp\*(C'\fR is not owned
Default is to assume that any \s-1UID\s0 less than or equal to 10 is a root
\& File::Temp->top_system_uid(10);
\& my $topid = File::Temp->top_system_uid;
This value can be adjusted to reduce security checking if required.
The value is only relevant when \f(CW\*(C`safe_level\*(C'\fR is set to \s-1MEDIUM\s0 or higher.
For maximum security, endeavour always to avoid ever looking at,
touching, or even imputing the existence of the filename. You do not
know that that filename is connected to the same file as the handle
you have, and attempts to check this can only trigger more race
conditions. It's far more secure to use the filehandle alone and
dispense with the filename altogether.
If you need to pass the handle to something that expects a filename
then, on a unix system, use \f(CW\*(C`"/dev/fd/" . fileno($fh)\*(C'\fR for arbitrary
programs, or more generally \f(CW\*(C`"+<=&" . fileno($fh)\*(C'\fR for Perl
programs. You will have to clear the close-on-exec bit on that file
descriptor before passing it to another process.
\& use Fcntl qw/F_SETFD F_GETFD/;
\& fcntl($tmpfh, F_SETFD, 0)
\& or die "Can't clear close-on-exec flag on temp fh: $!\en";
.Sh "Temporary files and \s-1NFS\s0"
.IX Subsection "Temporary files and NFS"
Some problems are associated with using temporary files that reside
on \s-1NFS\s0 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 \s-1NFS\s0 will not be as good as for
Originally began life in May 1999 as an \s-1XS\s0 interface to the system
\&\fImkstemp()\fR function. In March 2000, the OpenBSD \fImkstemp()\fR 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.
\&\*(L"tmpnam\*(R" in \s-1POSIX\s0, \*(L"tmpfile\*(R" in \s-1POSIX\s0, File::Spec, File::Path
See IO::File and File::MkTemp for different implementations of
Tim Jenness <t.jenness@jach.hawaii.edu>
Copyright (C) 1999\-2001 Tim Jenness and the \s-1UK\s0 Particle Physics and
Astronomy Research Council. All Rights Reserved. This program is free
software; you can redistribute it and/or modify it under the same
Original Perl implementation loosely based on the OpenBSD C code for
\&\fImkstemp()\fR. Thanks to Tom Christiansen for suggesting that this module
should be written and providing ideas for code improvements and
projects / OpenSPARC-T2-DV / blob