When writing a test or whenn running a build job it is usually a good practice to use a temporary directory and then clean up after the process is done.

It is also a good practice to make sure the temporary directoy is unique so if two processes run at the same time they won't interfere.

In Linux one usually has a directory called /tmp to store temporary files. In most of the programming languages there is some tool to create temporary directories. Sometimes these also handle the removal of these directories once they are not needed any more.

In Unix/Linux shell we can use the mktemp commmand to create a temporary directory inside the /tmp directory. 

mktemp -d -t ci-XXXXXXXXXX

The -d flag instructs the command to create the directory.

The -t flag allows us to provide a template. Each X character will be replaced by a random character. The more such characters the better your chances of having a unique directory. The rest of the template can and should be use to make it clear what is the purpose of the directory. In the above example this directory was created for and by the CI system.

The command will print the directory to the screen, but you can capture it to a variable and you can use it to create your files in this temporary directory. 

tmp_dir=$(mktemp -d -t ci-XXXXXXXXXX)

At the end of the process you will probably want to remove the directory.

Here is a full example:

examples/ci.sh

#!/bin/bash
tmp_dir=$(mktemp -d -t ci-XXXXXXXXXX)
echo $tmp_dir

# ...

rm -rf $tmp_dir

It will print the name of the directory that will look like this: 

/tmp/ci-9p1TBXRJZK

Date based directory

It can be also a good idea to include the date in the name of the directory. Especially if we might keep it for later observation. In any case here is an example on how to generate a temporary directory that has a fixed part, a date-based part, and a random part:

examples/ci-date.sh

#!/bin/bash
tmp_dir=$(mktemp -d -t ci-$(date +%Y-%m-%d-%H-%M-%S)-XXXXXXXXXX)

echo $tmp_dir

rm -rf $tmp_dir

The directory name will look like this: 

/tmp/ci-2019-01-11-11-48-34-KdQBLLObFw

Other root directory

By default the temporary directory will be created inside the /tmp directory. Sometimes we might want it to be in some other directory. For example I've created a tmp directory in my home directory and wanted to place the temporary directories inside that directory:

examples/ci-other.sh

#!/bin/bash
tmp_dir=$(mktemp -d -t ci-XXXXXXXXXX --tmpdir=/home/gabor/tmp)

echo $tmp_dir

rm -rf $tmp_dir

The path to the new directory will look like this: 

/home/gabor/tmp/ci-PWDTbA19TA

For further options you might want to check out the documentation of mktemp.