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MKTEMP(1)		OpenBSD	General	Commands Manual		     MKTEMP(1)

NAME
     mktemp -- make temporary filename (unique)

SYNOPSIS
     mktemp [-dqtu] [-p	directory] [template]

DESCRIPTION
     The mktemp	utility	takes the given	filename template and overwrites a
     portion of	it to create a unique filename.	 The template may be any file-
     name with at least	six `Xs' appended to it, for example
     /tmp/tfile.XXXXXXXXXX.  If	no template is specified a default of
     tmp.XXXXXXXXXX is used and	the -t flag is implied (see below).

     The trailing `Xs' are replaced with a unique digit	and letter combina-
     tion.  The	name chosen depends both on the	number of `Xs' in the template
     and the number of collisions with pre-existing files.  The	number of
     unique filenames mktemp can return	depends	on the number of `Xs' pro-
     vided; ten	`Xs' will result in mktemp testing roughly 26 ** 10 combina-
     tions.

     If	mktemp can successfully	generate a unique filename, the	file (or
     directory)	is created with	file permissions such that it is only readable
     and writable by its owner (unless the -u flag is given) and the filename
     is	printed	to standard output.

     mktemp is provided	to allow shell scripts to safely use temporary files.
     Traditionally, many shell scripts take the	name of	the program with the
     PID as a suffix and use that as a temporary filename.  This kind of nam-
     ing scheme	is predictable and the race condition it creates is easy for
     an	attacker to win.  A safer, though still	inferior approach is to	make a
     temporary directory using the same	naming scheme.	While this does	allow
     one to guarantee that a temporary file will not be	subverted, it still
     allows a simple denial of service attack.	For these reasons it is	sug-
     gested that mktemp	be used	instead.

     The options are as	follows:

     -d	     Make a directory instead of a file.

     -p	directory
	     Use the specified directory as a prefix when generating the tem-
	     porary filename.  The directory will be overridden	by the user's
	     TMPDIR environment	variable if it is set.	This option implies
	     the -t flag (see below).

     -q	     Fail silently if an error occurs.	This is	useful if a script
	     does not want error output	to go to standard error.

     -t	     Generate a	path rooted in a temporary directory.  This directory
	     is	chosen as follows:

	     +o	 If the	user's TMPDIR environment variable is set, the direc-
		 tory contained	therein	is used.

	     +o	 Otherwise, if the -p flag was given the specified directory
		 is used.

	     +o	 If none of the	above apply, /tmp is used.

	     In	this mode, the template	(if specified) should be a directory
	     component (as opposed to a	full path) and thus should not contain
	     any forward slashes.

     -u	     Operate in	``unsafe'' mode.  The temp file	will be	unlinked
	     before mktemp exits.  This	is slightly better than	mktemp(3) but
	     still introduces a	race condition.	 Use of	this option is not
	     encouraged.

     The mktemp	utility	exits with a value of 0	on success or 1	on failure.

ENVIRONMENT
     TMPDIR  directory in which	to place the temporary file when in -t mode

EXAMPLES
     The following sh(1) fragment illustrates a	simple use of mktemp where the
     script should quit	if it cannot get a safe	temporary file.

	   TMPFILE=`mktemp /tmp/example.XXXXXXXXXX` || exit 1
	   echo	"program output" >> $TMPFILE

     The same fragment with support for	a user's TMPDIR	environment variable
     can be written as follows.

	   TMPFILE=`mktemp -t example.XXXXXXXXXX` || exit 1
	   echo	"program output" >> $TMPFILE

     This can be further simplified if we don't	care about the actual name of
     the temporary file.  In this case the -t flag is implied.

	   TMPFILE=`mktemp` || exit 1
	   echo	"program output" >> $TMPFILE

     In	some cases, it may be desirable	to use a default temporary directory
     other than	/tmp.  In this example the temporary file will be created in
     /extra/tmp	unless the user's TMPDIR environment variable specifies	other-
     wise.

	   TMPFILE=`mktemp -p /extra/tmp example.XXXXXXXXXX` ||	exit 1
	   echo	"program output" >> $TMPFILE

     In	other cases, we	want the script	to catch the error.  For instance, if
     we	attempt	to create two temporary	files and the second one fails we need
     to	remove the first before	exiting.

	   TMP1=`mktemp	-t example.1.XXXXXXXXXX` || exit 1
	   TMP2=`mktemp	-t example.2.XXXXXXXXXX`
	   if [	$? -ne 0 ]; then
		   rm -f $TMP1
		   exit	1
	   fi

     Or	perhaps	you don't want to exit if mktemp is unable to create the file.
     In	this case you can protect that part of the script thusly.

	   TMPFILE=`mktemp -q -t example.XXXXXXXXXX` &&	{
		   # Safe to use $TMPFILE in this block
		   echo	data > $TMPFILE
		   ...
		   rm -f $TMPFILE
	   }

DIAGNOSTICS
     One of the	following error	messages may be	displayed if mktemp does not
     succeed and the -q	option was not specified:

     insufficient number of Xs in template
	     The specified template contained fewer than six `Xs' at the end.

     template must not contain directory separators in -t mode
	     The template contained one	or more	directory components and the
	     -t	option was specified.

     cannot make temp dir
	     mktemp was	unable to create the temporary directory for any of
	     the reasons specified by mkdtemp(3).

     cannot make temp file
	     mktemp was	unable to create the temporary file for	any of the
	     reasons specified by mkstemp(3).

     cannot allocate memory
	     mktemp was	unable to allocate memory for any of the reasons spec-
	     ified by malloc(3).

SEE ALSO
     mktemp(3)

HISTORY
     The mktemp	utility	first appeared in OpenBSD 2.1.

OpenBSD	5.8			March 27, 2017			   OpenBSD 5.8

NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT | EXAMPLES | DIAGNOSTICS | SEE ALSO | HISTORY

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