The mkdir (make directory) command in the Unix, DOS, OS/2, PHP, and Microsoft Windows operating systems is used to make a new directory. In DOS, OS/2 and Windows the command is often abbreviated to md.

Normal usage is as straightforward as follows:

<source lang="bash"> mkdir name_of_directory </source>

Where name_of_directory is the name of the directory one wants to create. When typed as above (i.e. normal usage), the new directory would be created within the current directory. On Unix, multiple directories can be specified, and mkdir will try to create all of them.

On Unix-like operating systems, mkdir takes options. Three of the most common options are:

-p is most often used when using mkdir to build up complex directory hierarchies, in case a necessary directory is missing or already there. -m is commonly used to lock down temporary directories used by shell scripts.

An example of -p in action is:

<source lang="bash"> mkdir -p /tmp/a/b/c </source>

If /tmp/a exists but /tmp/a/b does not, mkdir will create /tmp/a/b before creating /tmp/a/b/c.