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 filename with some number of 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 combination of the cur- rent process number and random letters. 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 provided; ten Xs will result in mktemp testing roughly 26 10 combinations.

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 stan- dard output.

mktemp is provided to allow shell scripts to safely use tem- porary 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 naming scheme is pre- dictable 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 suggested that mktemp be used instead.

The options are as follows
  • d Make a directory instead of a file.
  • p directoryUse the specified directory as a prefix when generat-ing the temporary filename. The directory will beoverridden 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:

If the user's TMPDIR environment variable is set, the directory contained therein is used.

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

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 bet- ter than mktemp(3) but still introduces a race condi- tion. Use of this option is not encouraged.

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

Debian packages using mktemp in maintainer scripts must depend on debianutils


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

TMPFILE=`mktemp -t example.XXXXXXXXXX` || exit 1 echo 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 In some cases, it may be desirable to use a default tempo- rary directory other than /tmp. In this example the tempo- rary file will be created in /extra/tmp unless the user's TMPDIR environment variable specifies otherwise.

TMPFILE=`mktemp -p /extra/tmp example.XXXXXXXXXX` || exit 1 echo In some 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.



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


mkdtemp(3)?, mkstemp(3), mktemp(3) HISTORY

The mktemp utility appeared in OpenBSD 2.1.

BSD September 30, 2001 1

This page is a man page (or other imported legacy content). We are unable to automatically determine the license status of this page.