Temp(3)               User Contributed Perl Documentation              Temp(3)

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

         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 );

       "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 implementa-
       tions of the mkstemp() family of functions are provided. These are,
       mkstemp(), mkstemps(), mkdtemp() and mktemp().

       Additionally, implementations of the standard POSIX tmpnam() and tmp-
       file() 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.

       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

       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 tempo-
       rary 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 tempo-
           rary 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.

           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

           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

            $fh->unlink_on_destroy( 1 );

           Default is for the file to be removed.

           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

       This section describes the recommended interface for generating tempo-
       rary files and directories.

           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 applica-
           tions.  But see the WARNING at the end.

             ($fh, $filename) = tempfile($template, DIR => $dir);

           Translates the template as before except that a directory name is

             ($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 cre-

           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 automati-
           cally 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() else-
           where in this document).  This is the preferred mode of operation,
           as if you only have a filehandle, you can never create a race con-
           dition 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 else-
           where in this document if opening the file is not required.

           Options can be combined as required.

           Will croak() if there is an error.

           This is the recommended interface for creation of temporary direc-
           tories.  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 tem-

             $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 par-
           ent 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 tem-
           plate 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 (other-
           wise 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 cre-
           ated in tmpdir() and will also be removed at program exit.

           Will croak() if there is an error.

       The following functions are Perl implementations of the mktemp() family
       of temp file generation system calls.

           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.

           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.

           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.

           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.

       This section describes the re-implementation of the tmpnam() and tmp-
       file() functions described in POSIX using the mkstemp() from this mod-

       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.

           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 con-

           See "tmpdir" in File::Spec for information on the choice of tempo-
           rary directory for a particular operating system.

           Will croak() if there is an error.

           Returns the filehandle of a temporary file.

             $fh = tmpfile();

           The file is removed when the filehandle is closed or when the pro-
           gram exits. No access to the filename is provided.

           If the temporary file can not be created undef is returned.  Cur-
           rently this command will probably not work when the temporary
           directory is on an NFS file system.

           Will croak() if there is an error.

       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 "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 condi-

           Will croak() if there is an error.

       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 stat() are com-
           pared).  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 file-
           name 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

           On some platforms, for example Windows NT, it is not possible to
           unlink an open file (the file must be closed first). On those plat-
           forms, 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

           This function should not be called if you are using the object ori-
           ented interface since the it will interfere with the object
           destructor deleting the file.

           Compare "stat" of filehandle with "stat" of provided filename.
           This can be used to check that the filename and filehandle ini-
           tially 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 usu-
           ally overcome by waiting a while after writing to the tempfile
           before attempting to "unlink0" it).

           Not exported by default.

           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 inter-

           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()

           Calling this function will cause any temp files or temp directories
           that are registered for removal to be removed. This happens auto-
           matically 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


           Not exported by default.

       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.
           Options are:

                   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 condi-
                   tions 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 direc-
                   tory in the path is checked in turn for safeness, recur-
                   sively 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 ver-
           sions 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 differ-
           ent 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 fail-
           ing on systems where the extra tests are irrelevant.

           If you really need to see whether the change has been accepted sim-
           ply 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;

           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

           Default is to assume that any UID less than or equal to 10 is a
           root UID.

             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

           Controls whether temporary files and directories should be retained
           regardless of any instructions in the program to remove them auto-
           matically.  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 tem-
           porary file, set this variable and expect the temp file to still be
           around when the program exits.

           Controls whether debugging messages should be enabled.

             $File::Temp::DEBUG = 1;

           Default is for debugging mode to be disabled.

       For maximum security, endeavour always to avoid ever looking at, touch-
       ing, 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 per-
       formance of I/O operations over NFS will not be as good as for a local


       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.


       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.

       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.

       "tmpnam" in POSIX, "tmpfile" in POSIX, File::Spec, File::Path

       See IO::File and File::MkTemp, Apache::TempFile for different implemen-
       tations of temporary file handling.

       Tim Jenness <>

       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 secu-
       rity enhancements.

perl v5.8.6                       2007-01-21                           Temp(3)