NAME

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

SYNOPSIS

use File::Temp qw/ tempfile tempdir /; 

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

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

$fh = tempfile();

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

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. 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.

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, $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 using the template. Trailing `X' characters are replaced with random letters to generate the filename. At least four `X' characters must be present in 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.

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 (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.

(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.

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, creat 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.

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 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's 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

In scalar context, 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.

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 checking that the filename and filehandle initially point to the same file and that the number of links to the file is 1. 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.

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.

Will not work on platforms that do not support the POSIX _PC_CHOWN_RESTRICTED symbol (for example, Windows NT).

The level can be changed as follows:

File::Temp->safe_level( File::Temp::HIGH );

The level constants are not exported by the module.

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.

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";

HISTORY

Originally began life in May 1999 as an XS interface to the system mkstemp() function. In March 2000, the 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.

SEE ALSO

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

See File::MkTemp for a different implementation of temporary file handling.

AUTHOR

Tim Jenness <t.jenness@jach.hawaii.edu>

Copyright (C) 1999, 2000 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.

cpanm File::Temp

perl -MCPAN -e shell
install File::Temp