Manual Pages for UNIX Darwin command on man File::Temp

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

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 );

$unopenedfile = mktemp( $template );

POSIX functions:

use File::Temp qw/ :POSIX /;

$file = tmpnam();

$fh = tmpfile();

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

Compatibility functions:

$unopenedfile = 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 inter-

face. 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 "safelevel" 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.

OOBBJJEECCTT-OORRIIEENNTTEEDD IINNTTEERRFFAACCEE

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 tempo-

rary file. nneeww 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. ffiilleennaammee 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. uunnlliinnkkoonnddeessttrrooyy Control whether the file is unlinked when the object goes out of

scope. The file is removed if this value is true and $KEEPALL is

not.

$fh->unlinkondestroy( 1 );

Default is for the file to be removed. DDEESSTTRROOYY 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 $KEEPALL is true, the file will not be

removed. FFUUNNCCTTIIOONNSS

This section describes the recommended interface for generating tempo-

rary files and directories. tteemmppffiillee

This is the basic function to generate temporary files. The behav-

iour 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 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

$KEEPALL). 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 $KEEPALL is true when the temp file is cre-

ated).

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 "OTEMPORARY" 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. tteemmppddiirr

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-

plate.

$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. MMKKTTEEMMPP FFUUNNCCTTIIOONNSS The following functions are Perl implementations of the mktemp() family of temp file generation system calls. mmkksstteemmpp 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. mmkksstteemmppss 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 testhGjiw.dat. Returns just the filehandle alone when called in scalar context. mmkkddtteemmpp Create a directory from a template. The template must end in X's that are replaced by the routine.

$tmpdirname = mkdtemp($template);

Returns the name of the temporary directory created. Returns undef on failure. Directory must be removed by the caller. mmkktteemmpp Returns a valid temporary filename but does not guarantee that the file will not be opened by someone else.

$unopenedfile = mktemp($template);

Template is the same as that required by mkstemp(). PPOOSSIIXX FFUUNNCCTTIIOONNSS

This section describes the re-implementation of the tmpnam() and tmp-

file() functions described in POSIX using the mkstemp() from this mod-

ule. Unlike the POSIX implementations, the directory used for the temporary file is not specified in a system include file ("Ptmpdir") 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. ttmmppnnaamm 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-

ditions.

See "tmpdir" in File::Spec for information on the choice of tempo-

rary directory for a particular operating system. ttmmppffiillee 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. AADDDDIITTIIOONNAALL FFUUNNCCTTIIOONNSS 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. tteemmppnnaamm 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 "OCREAT | OEXCL" 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-

tions. UUTTIILLIITTYY FFUUNNCCTTIIOONNSS Useful functions for dealing with the filehandle and filename. uunnlliinnkk00 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. 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 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 $KEEPALL 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. ccmmppssttaatt 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. 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. uunnlliinnkk11 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-

face. Not exported by default.

This function is disabled if the global variable $KEEPALL is true.

cclleeaannuupp 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 files).

File::Temp::cleanup();

Not exported by default. PPAACCKKAAGGEE VVAARRIIAABBLLEESS These functions control the global state of the package. ssaaffeelleevveell 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. 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 "PCCHOWNRESTRICTED" 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->safelevel( 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 5.00503 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 "safelevel".

$newlevel = File::Temp->safelevel( 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->topsystemuid(10);

my $topid = File::Temp->topsystemuid;

This value can be adjusted to reduce security checking if required. The value is only relevant when "safelevel" is set to MEDIUM or higher.

$$KKEEEEPPAALLLL

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::KEEPALL = 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.

$$DDEEBBUUGG

Controls whether debugging messages should be enabled.

$File::Temp::DEBUG = 1;

Default is for debugging mode to be disabled. WWAARRNNIINNGG

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/FSETFD FGETFD/;

fcntl($tmpfh, FSETFD, 0)

or die "Can't clear close-on-exec flag on temp fh: $!\n";

TTeemmppoorraarryy ffiilleess aanndd NNFFSS 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 disk. FFoorrkkiinngg

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. BBIINNMMOODDEE

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.