mktemp

Make a temporary file.

Syntax
      mktemp [-d] [-q] [-t prefix] [-u] template ...

      mktemp [-d] [-q] [-u] -t prefix

Options
   -d      Make a directory instead of a file.

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

   -t prefix
           Generate a template (using the supplied prefix and TMPDIR if set)
           to create a filename template.

   -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 takes each of the given file name templates and overwrites a portion of it to create a file name. This file name is unique and suitable for use by the application. The template may be any file name with some number of 'Xs' appended to it, for example /tmp/temp.XXXX. The trailing 'Xs' are replaced with the current process number and/or a unique letter combination.

The number of unique file names mktemp can return depends on the number of 'Xs' provided; six 'Xs' will result in mktemp selecting 1 of 56800235584 (62 ** 6) possible file names. On case-insensitive file systems, the effective number of unique names is significantly less; given six 'Xs', mktemp will instead select 1 of 2176782336 (36 ** 6) possible unique file names.

If mktemp can successfully generate a unique file name, the file is created with mode 0600 (unless the -u flag is given) and the filename is printed to standard output. If the -t prefix option is given, mktemp will generate a template string based on the prefix and the _CS_DARWIN_USER_TEMP_DIR configuration variable if available. Fallback locations if _CS_DARWIN_USER_TEMP_DIR is not available are TMPDIR and /tmp.

Care should be taken to ensure that it is appropriate to use an environment variable potentially supplied by the user. If no arguments are passed or if only the -d flag is passed mktemp behaves as if -t tmp was supplied.

Any number of temporary files may be created in a single invocation, including one based on the internal template resulting from the -t flag.

The mktemp utility 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 file name. This kind of naming 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 suggested that mktemp be used instead.

EXIT Status The mktemp utility exits 0 on success, and >0 if an error occurs.

Examples

Create a temp file and store the filename in $SCRATCH:
$ SCRATCH=$(mktemp -t tmp.XXXXXXXXXX)

Delete the file:
$ rm -f "$SCRATCH"

Script fragment to create a temp file and quit if unable to get a safe temporary file.

tempfoo='basename $0'
TMPFILE='mktemp /tmp/${tempfoo}.XXXXXX' || exit 1
echo "program output" >> $TMPFILE

"If you want to make an apple pie from scratch, you must first create the universe" ~ Dr. Carl Sagan

Related linux commands:

chmod - Change access permissions.
stat - Display the status of a file.


 
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