Provided by: perl-doc_5.26.1-6ubuntu0.7_all 
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.