Files and directories

`mktemp`

Create a temporary file or directory with a unique, unpredictable name and print that name.

mktemp [OPTION...] [TEMPLATE]

8 of 8 examples run in Debian 13.7 on 2026-10-31 · coreutils 9.7-3 · manual: mktemp(1)

Scripts that need scratch space should never use a fixed name like /tmp/output.txt: two runs at once would overwrite each other, and on a shared machine another user could create that name first as a symlink to something of yours. mktemp creates the file atomically with a random name, mode 600 (owner only), and prints the name so you can capture it.

The pattern every script should know is: create with mktemp, store the name in a variable, and delete it in an EXIT trap so it is cleaned up however the script ends. mktemp -d does the same for a directory, which is handy when you need several files.

Files go in $TMPDIR if set, otherwise /tmp. A template controls the name: its run of Xs (at least three) is replaced with random characters. Without one, the name is tmp. plus ten random characters.

Examples

Create a temporary file

$ f=$(mktemp)
> echo "$f"
> ls -l "$f"

output

/tmp/tmp.HF7YSqL4Lb
-rw------- 1 dev dev 0 Oct 31 20:20 /tmp/tmp.HF7YSqL4Lb

The name is random (tmp. plus ten characters) and differs on every run. The file exists, is empty and is readable only by its owner.

Create a temporary directory

$ d=$(mktemp -d)
> ls -ld "$d"

output

drwx------ 2 dev dev 2 Oct 31 20:20 /tmp/tmp.gORisNblxV

-d creates a directory with mode 700, a private workspace for several files.

Clean up automatically when the script exits

job.sh

#!/bin/bash
set -euo pipefail
work=$(mktemp -d)
trap 'rm -rf -- "$work"' EXIT
sort data/fruits.txt | uniq -c > "$work/counts"
echo "working in $work"
head -3 "$work/counts"

$ bash job.sh
> ls /tmp

output

working in /tmp/tmp.mw6TXfuzy9
      3 apple
      2 banana
      2 cherry

The EXIT trap runs when the script ends for any reason, including an error under set -e, so the directory is removed. The final ls shows /tmp empty again.

Choose a recognizable name

$ mktemp /tmp/backup-XXXXXX.log
> mktemp --suffix=.csv /tmp/export-XXXXXXXX

output

/tmp/backup-4zjz15.log
/tmp/export-TXIOIVEn.csv

The run of Xs is replaced with random characters. When text follows the Xs, GNU mktemp keeps it as a suffix; --suffix says so explicitly. A recognizable prefix tells you which program left a file behind.

Create the file in a specific directory

$ mkdir scratch
> mktemp -p scratch
> TMPDIR=$PWD/scratch mktemp -t report.XXXX

output

scratch/tmp.tmdINgeKHj
/home/dev/demo/scratch/report.6yKB

-p DIR puts the file in DIR. With -t, the template is placed in $TMPDIR, which is how you let users point temporary files at a bigger disk.

Generate a name without creating anything

$ name=$(mktemp -u)
> echo "$name"
> ls "$name"

outputexit 2

/tmp/tmp.X07fxWaKjK
ls: cannot access '/tmp/tmp.X07fxWaKjK': No such file or directory

-u only prints a name. Nothing is created, as the failing ls shows, so another process could take that name before you do: avoid -u except for things like named pipes that you create right away.

Replace a file atomically

$ tmp=$(mktemp data/config.json.XXXXXX)
> jq '.version = "2.5.0"' data/config.json > "$tmp" && mv "$tmp" data/config.json
> jq .version data/config.json

output

"2.5.0"

Writing to a temporary file in the same directory and then renaming it with mv means readers see either the old file or the new one, never a half-written one. Note that the new file keeps mktemp's 600 mode.

Too few X's in the template

$ mktemp /tmp/run-XX

explain

outputexit 1

mktemp: too few X's in template ‘/tmp/run-XX’

The template needs at least three Xs to give enough randomness; GNU mktemp refuses shorter ones.

Common pitfalls

touch /tmp/myscript.$$ is not a safe substitute: process IDs are predictable, and the file is created with your normal umask instead of 600.
Forgetting cleanup leaves files behind on every run, including failed ones. Put the trap ... EXIT right after the mktemp.
Files from mktemp are mode 600; if you mv one into place as a config file that others must read, chmod it first.

GNU vs BSD and macOS

The examples above ran the GNU/Linux version. These are the differences that matter on macOS and the BSDs (written from their documentation, not run here).

On BSD/macOS, -t takes a prefix rather than a template, and the default name format differs. A full template such as mktemp /tmp/foo.XXXXXX (X's at the end) behaves the same on both.
--suffix and -p are GNU options.

Options worth knowing

A selection, described in our own words. For the full list, see mktemp(1) or mktemp --help.

Option	What it does
`-d, --directory`	Create a directory instead of a file.
`-u, --dry-run`	Only print a name; create nothing (unsafe).
`-q, --quiet`	Do not print an error if creation fails.
`-p DIR`	Create the file in DIR instead of $TMPDIR or /tmp.
`--tmpdir[=DIR]`	Like -p; without DIR, use $TMPDIR or /tmp.
`-t`	Interpret the template relative to $TMPDIR or /tmp.
`--suffix SUFF`	Append SUFF to the template; the X's must come before it.

Examples

Common pitfalls

GNU vs BSD and macOS

Options worth knowing

Related