How to mkdir only if a directory does not already exist?

Question

I am writing a shell script to run under the KornShell (ksh) on AIX. I would like to use the mkdir command to create a directory. But the directory may already exist, in which case I do not want to do anything. So I want to either test to see that the directory does not exist, or suppress the "File exists" error that mkdir throws when it tries to create an existing directory.

How can I best do this?

Solution 1

Try mkdir -p:

mkdir -p foo

Note that this will also create any intermediate directories that don't exist; for instance,

mkdir -p foo/bar/baz

will create directories foo, foo/bar, and foo/bar/baz if they don't exist.

Some implementation like GNU mkdir include mkdir --parents as a more readable alias, but this is not specified in POSIX/Single Unix Specification and not available on many common platforms like macOS, various BSDs, and various commercial Unixes, so it should be avoided.

If you want an error when parent directories don't exist, and want to create the directory if it doesn't exist, then you can test for the existence of the directory first:

[ -d foo ] || mkdir foo

Solution 2

This should work:

$ mkdir -p dir

or:

if [[ ! -e $dir ]]; then
    mkdir $dir
elif [[ ! -d $dir ]]; then
    echo "$dir already exists but is not a directory" 1>&2
fi

which will create the directory if it doesn't exist, but warn you if the name of the directory you're trying to create is already in use by something other than a directory.

Solution 3

Use the -p flag.

man mkdir
mkdir -p foo

Solution 4

Defining complex directory trees with one command

mkdir -p project/{lib/ext,bin,src,doc/{html,info,pdf},demo/stat/a}

Solution 5

If you don't want to show any error message:

[ -d newdir ] || mkdir newdir

If you want to show your own error message:

[ -d newdir ] && echo "Directory Exists" || mkdir newdir

View more solutions

Comments

[Alnitak]

wrong on both counts, AFAIK. tests return true on success, and -d exists too (at least on MacOS X)

[Mike Q]

This will fail if "tmp" did not exist. nor does it give you any confirmation.

[Mike Q]

the shortened example you use is exactly what you should not do. It is reversing the logic to save coding space but it should use ! and && and make more sense to those reading it.

[angularsen]

On Windows8 it seems -p is no longer supported and it's the default behavior.

[Brian Campbell]

@AndreasLarsen This question is about mkdir on Unix-like systems, not on Windows. -p is required for POSIX/Single Unix Specification compliance, so anything that intents to comply with those specifications will support -p. Windows is entirely different, unless you use a POSIX emulation layer like Cygwin or MSYS.

[Justin L.]

it might be worth mentioning that this isn't quite thread-safe. between the time that you check if the directory exists and the time you try to write, things might change.

[uliwitness]

As mentioned by @BrianCampbell, this will also create any other directories in the path. This can be dangerous if e.g. a volume becomes unmounted, as it may create directories in the mount point.

[herve]

I discovered something interesting today with mkdir -p, you can use brackets! {} to create "complex" directory tree in a command. See here: technosophos.com/2010/04/15/…

[rudimeier]

@MikeQ I 'd prefer || instead of && because then the whole line has the right exit status. Important if your shell runs with errexit or if that line is the last one in a function, switch-case, whatever.

[Zsigmond Lőrinczy]

Or: mkdir somedir 2>/dev/null || true

[Fedir RYKHTIK]

no error if existing, make parent directories as needed

[Daniel Kamil Kozar]

Keep in mind that this is not a feature of mkdir itself, but the shell that executes the command. It's called brace expansion - AFAIK, only Bash, ksh, zsh, and the C shell support it.

[J. Chomel]

OP was about AIX kornshell... nothing to do with Windows, does it?

[Atlas7]

if you have spaces around the commas you may (will) get unexpected result. Beware.

[chepner]

@herve That has nothing to do with mkdir; the shell expands such an expression to a discrete list of argument that are passed to mkdir.

[John Hamilton]

@Atlas7 stated, you will need to escape characters that are normally part of regex. (i.e. instead of using folder name you need to use folder\ name)

[pedram bashiri]

Is there any advantage in using if loop!? why would someone choose that over -p option?!

[AbhinavVaidya8]

I have shared you ways of creating the folders when an folder does not exists. It depends upon the requirement on the one. If you have a use case where you need to check if folder does not exist and you want to keep track of that so you can go with solution 1. If it does not matter, you can go with solution 2, it will create the folder if not exists.

[akozi]

Does this work with a wild card before the intermediate steps? Ex /*/foo/bar/baz ?

[Brian Campbell]

@akozi Yes, if the appropriate directories already exist at the level that the wild card is used. In the shell, glob expansion happens before passing the arguments to the program (mkdir, in this case). So if you had directories a, b, and c, mkdir -p */foo/bar/baz would be the same as mkdir -p a/foo/bar/baz b/foo/bar/baz c/foo/bar/baz. mkdir can take multiple arguments, and when given -p, it will create needed intermediate directories. Experiment with this yourself. Try echo mkdir -p */foo/bar/baz to see what command is run; or just try running it in a test directory.

[Chris Page]

This is not an answer; this is a separate topic that would be more appropriate as a comment.

[Peter Mortensen]

Race conditions? Can you elaborate in your answer? Non-atomic test & create?

[Peter Mortensen]

Defining? Do you mean creating?

[Peter Mortensen]

But subject to race conditions?

[Peter Mortensen]

Are you sure it was supported before? Do you have a source?

[paxdiablo]

@Peter, a snippet like (for example) [ -d newdir ] || mkdir newdir, where the directory does not initially exist, has a race condition in that, between the test for existence and the attempted creation, another process could swoop in and create the directory. Hence the mkdir would then fail.

[Jahid]

@PeterMortensen : Of course. Use mkdir -p if you do not want race conditions. But you won't get to show your own Directory exists error.

[RicarHincapie]

@herve discovery is very handy. Please remember not to leave whitespaces in any part of this script.

[Shankara Narayana]

-p, --parents no error if existing, make parent directories as needed

[hakre]

@Mike Q: the base path /tmp has likely been chosen in the example to represent a base-path that always exists and is write-able to the current user, e.g. the user has enough rights to create a directory in. You raise a valid point thought:: the logic is a bit contradictory, as when this command fails, it can mean two things: 1.) the directory exists or 2.) the directory could not be created. This is not true for the operation itself, therefore a simple post-check on the directory path can give the confirmation, or the next command that operates on.

[edoardesd]

It should be: mkdir -p /my/new/dir >/dev/null 2>&1

[Leevi L]

mkdir -p my/new/dir does not complain if my/new/dir already exists, no need to redirect output

[moodboom]

Typo fixed. Leevi, I believe I ran into a situation where the output needed to be squelched.

[Jesse Nickles]

mkdir -p /tmp/qq > /dev/null 2>&1 will create /tmp/ if missing.

[dube]

note for naiive windows users: -p still fails on windows when the folder exists

[Jeppe]

@herve Awesome! Just realized it works for other commands as well, e.g. to create 3 files: touch {a,b,c}.txt