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

问题

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.

Any thoughts on how best to do this?

回答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

回答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.

回答3:

Use the -p flag.

man mkdir
mkdir -p foo

回答4:

Defining complex directory trees with one command

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

回答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

回答6:

The old tried and true

mkdir /tmp/qq >/dev/null 2>&1

will do what you want with none of the race conditions many of the other solutions have.

Sometimes the simplest (and ugliest) solutions are the best.

回答7:

mkdir foo works even if the directory exists. To make it work only if the directory named "foo" does not exist, try using the -p flag.

Example :-

mkdir -p foo

This will create the directory named "foo" only if it does not exist. :)

回答8:

directory_name = "foo"

if [ -d $directory_name ]
then
    echo "Directory already exists"
else
    mkdir $directory_name
fi

回答9:

Or if you want to check for existence first:

if [[ ! -e /path/to/newdir ]]; then
            mkdir /path/to/newdir
fi

-e is the exist test for korn shell.

You can also try googling a korn shell manual.

回答10:

mkdir does not support -p switch anymore on Windows 8+ systems.

You can use this:

IF NOT EXIST dir_name MKDIR dir_name

回答11:

You can either use if loop to check if directory exists or not, if it does not exits than create the directory.

1) dir=/home/dir_name

if [ ! -d $dir ]
then
     mkdir $dir
else
     echo "Directory exists"  
fi

2) You can directory use mkdir with -p option to create a directory. It will check if the directory is not available it will.

mkdir -p $dir

mkdir -p also allows to create the tree structure of the directory. If you want to create the parent and child directories using same command, can opt mkdir -p

mkdir -p /home/parent_dir /home/parent_dir/child1 /home/parent_dir/child2

回答12:

Referring to man page man mkdir for option -p

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

which will create all directories in a given path, if exists throws no error otherwise it creates all directories from left to right in the given path. Try the below command. the directories newdir and anotherdir doesn't exists before issuing this command

Correct Usage

mkdir -p /tmp/newdir/anotherdir

After executing the command you can see newdir and anotherdir created under /tmp. You can issue this command as many times you want, the command always have exit(0). Due to this reason most people use this command in shell scripts before using those actual paths.

回答13:

This is a simple function (bash shell) which lets you create a directory if it doesn't exist.

#----------------------------------
# Create a directory if it doesn't exist
#------------------------------------
createDirectory() {
    if [ ! -d $1 ]
        then
        mkdir -p $1
    fi
}

You can call the above function as :

createDirectory /tmp/fooDir/BarDir

The above creates fooDir and BarDir if they don't exist. Note the "-p" option in mkdir command which creates directories recursively. Hope this helps.