MirOS Manual: File::Temp(3p)


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

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 /;

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       $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 open-
     ing.  Additional security levels are provided to check, for
     example, that the sticky bit is set on world writable direc-
     tories.  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.

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     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 TEM-
         PLATE 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

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         not be removed.

FUNCTIONS

     This section describes the recommended interface for gen-
     erating 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 direc-
         tory 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

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         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 tem-
         porary 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 tem-
         plate 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.

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           $tempdir = tempdir ( DIR => $dir );

         Specifies the directory to use for the temporary direc-
         tory. 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 specifica-
         tions 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 direc-
         tory 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 tem-
         plate, 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 direc-
         tory 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 );

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         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 tem-
         plate.

           ($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 guaran-
         tee 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

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     ("P_tmpdir") but simply depends on the choice of tmpdir()
     returned by File::Spec. On some implementations this loca-
     tion 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 con-
         tinue 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 tem-
         plate.

           ($fh, $file) = tmpnam();

         If possible, this form should be used to prevent possi-
         ble race conditions.

         See "tmpdir" in File::Spec for information on the choice
         of temporary directory for a particular operating sys-
         tem.

         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.

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     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 secu-
         rity 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

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         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 sup-
         ported. 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 Win-
         dows.  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

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         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 condi-
                 tions are avoided.  Finally the unlink0 function
                 is used to remove files safely.

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         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() givea-
                 way'' using the POSIX sysconf() function. If
                 this is a possibility, each directory 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, Win-
                 dows 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 sim-
         ply 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 dif-
         ferent 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;

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     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 pro-
         gram 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 vari-
         able 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.

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     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

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     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 dif-
     ferent implementations of temporary file handling.

AUTHOR

     Tim Jenness <tjenness@cpan.org>

     Copyright (C) 1999-2007 Tim Jenness and the UK Particle Phy-
     sics 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 suggest-
     ing that this module should be written and providing ideas
     for code improvements and security enhancements.

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