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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 ();

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

         $tmp = new File::Temp( UNLINK => 0, SUFFIX => '.dat' );
         print $tmp "Some data\n";
         print "Filename is $tmp\n";

       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.

       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. Addition-
           ally, 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.

       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() func-
           tion 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 doc-
           ument).  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 con-
           junction with UNLINK set to true. Default is to always open the file to protect from possible race condi-
           tions. 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.

       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 spec-
           ifications 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 direc-
           tory 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.

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.

       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.

       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.  Returns undef on failure.

           Directory must be removed by the caller.

       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().

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 imple-
       mentations 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.

       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.

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.

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 check-
           ing 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. 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.

       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.

           On certain platofms, eg 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 attempt-
           ing 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.

       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 pro-
           grams 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.

       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, Apachae::TempFile for different implementations of temporary file handling.

AUTHOR
       Tim Jenness <tjennessATcpan.org>

       Copyright (C) 1999-2005 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 enhance-
       ments.



perl v5.8.8                       2001-09-21                     File::Temp(3)