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File::Temp(3)	       Perl Programmers Reference Guide		 File::Temp(3)

NAME
       File::Temp - return name and handle of a temporary file safely

SYNOPSIS
	 use File::Temp qw/ tempfile tempdir /;

	 $fh = tempfile();
	 ($fh, $filename) = tempfile();

	 ($fh, $filename) = tempfile( $template, DIR => $dir);
	 ($fh, $filename) = tempfile( $template, SUFFIX => '.dat');

	 $dir = tempdir( CLEANUP => 1 );
	 ($fh, $filename) = tempfile( DIR => $dir );

       Object interface:

	 require File::Temp;
	 use File::Temp ();
	 use File::Temp qw/ :seekable /;

	 $fh = new File::Temp();
	 $fname = $fh->filename;

	 $fh = new File::Temp(TEMPLATE => $template);
	 $fname = $fh->filename;

	 $tmp = new File::Temp( 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.

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. Also, the
       object is configured such that it stringifies to the name of the
       temporary file, and can be compared to a filename directly. The object
       isa "IO::Handle" and isa "IO::Seekable" so all those methods are
       available.

       new Create a temporary file object.

	     my $tmp = new File::Temp();

	   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 and SUFFIX. Additionally, the filename
	   template is specified using the TEMPLATE option. The OPEN option is
	   not supported (the file is always opened).

	    $tmp = new File::Temp( TEMPLATE => 'tempXXXXX',
				   DIR => 'mydir',
				   SUFFIX => '.dat');

	   Arguments are case insensitive.

	   Can call croak() if an error occurs.

       filename
	   Return the name of the temporary file associated with this object.

	     $filename = $tmp->filename;

	   This method is called automatically when the object is used as a
	   string.

       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 global variable $KEEP_ALL is true, the file 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, 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( $template, 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.

	   Options can be combined as required.

	   Will croak() if there is an error.

       tempdir
	   This is the recommended interface for creation of temporary
	   directories.	 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.

	   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 the umask() 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.

	   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, use ""/dev/fd/" . fileno($fh)" for arbitrary
       programs, or more generally ""+<=&" . fileno($fh)" 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: $!\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.

       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.

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.

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.

AUTHOR
       Tim Jenness <tjenness@cpan.org>

       Copyright (C) 1999-2007 Tim Jenness and the UK 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 terms
       as Perl itself.

       Original Perl implementation loosely based on the OpenBSD C code for
       mkstemp(). Thanks to Tom Christiansen for suggesting that this module
       should be written and providing ideas for code improvements and
       security enhancements.

perl v5.10.0			  2007-12-18			 File::Temp(3)
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