Create a Directory If It Doesn't Exist

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

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

How to create a directory if it doesn't exist using Node.js

For individual dirs:

var fs = require('fs');
var dir = './tmp';

if (!fs.existsSync(dir)){
    fs.mkdirSync(dir);
}

Or, for nested dirs:

var fs = require('fs');
var dir = './tmp/but/then/nested';

if (!fs.existsSync(dir)){
    fs.mkdirSync(dir, { recursive: true });
}

Create a directory if it does not exist and then create the files in that directory as well

This code checks for the existence of the directory first and creates it if not, and creates the file afterwards. Please note that I couldn't verify some of your method calls as I don't have your complete code, so I'm assuming the calls to things like getTimeStamp() and getClassName() will work. You should also do something with the possible IOException that can be thrown when using any of the java.io.* classes - either your function that writes the files should throw this exception (and it be handled elsewhere), or you should do it in the method directly. Also, I assumed that id is of type String - I don't know as your code doesn't explicitly define it. If it is something else like an int, you should probably cast it to a String before using it in the fileName as I have done here.

Also, I replaced your append calls with concat or + as I saw appropriate.

public void writeFile(String value){
    String PATH = "/remote/dir/server/";
    String directoryName = PATH.concat(this.getClassName());
    String fileName = id + getTimeStamp() + ".txt";

    File directory = new File(directoryName);
    if (! directory.exists()){
        directory.mkdir();
        // If you require it to make the entire directory path including parents,
        // use directory.mkdirs(); here instead.
    }

    File file = new File(directoryName + "/" + fileName);
    try{
        FileWriter fw = new FileWriter(file.getAbsoluteFile());
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(value);
        bw.close();
    }
    catch (IOException e){
        e.printStackTrace();
        System.exit(-1);
    }
}

You should probably not use bare path names like this if you want to run the code on Microsoft Windows - I'm not sure what it will do with the / in the filenames. For full portability, you should probably use something like File.separator to construct your paths.

Edit: According to a comment by JosefScript below, it's not necessary to test for directory existence. The directory.mkdir() call will return true if it created a directory, and false if it didn't, including the case when the directory already existed.

How can I safely create a nested directory?

On Python ≥ 3.5, use pathlib.Path.mkdir:

from pathlib import Path
Path("/my/directory").mkdir(parents=True, exist_ok=True)

For older versions of Python, I see two answers with good qualities, each with a small flaw, so I will give my take on it:

Try os.path.exists, and consider os.makedirs for the creation.

import os
if not os.path.exists(directory):
    os.makedirs(directory)

As noted in comments and elsewhere, there's a race condition – if the directory is created between the os.path.exists and the os.makedirs calls, the os.makedirs will fail with an OSError. Unfortunately, blanket-catching OSError and continuing is not foolproof, as it will ignore a failure to create the directory due to other factors, such as insufficient permissions, full disk, etc.

One option would be to trap the OSError and examine the embedded error code (see Is there a cross-platform way of getting information from Python’s OSError):

import os, errno

try:
    os.makedirs(directory)
except OSError as e:
    if e.errno != errno.EEXIST:
        raise

Alternatively, there could be a second os.path.exists, but suppose another created the directory after the first check, then removed it before the second one – we could still be fooled.

Depending on the application, the danger of concurrent operations may be more or less than the danger posed by other factors such as file permissions. The developer would have to know more about the particular application being developed and its expected environment before choosing an implementation.

Modern versions of Python improve this code quite a bit, both by exposing FileExistsError (in 3.3+)...

try:
    os.makedirs("path/to/directory")
except FileExistsError:
    # directory already exists
    pass

...and by allowing a keyword argument to os.makedirs called exist_ok (in 3.2+).

os.makedirs("path/to/directory", exist_ok=True)  # succeeds even if directory exists.

If a folder does not exist, create it

As others have said, use System.IO.Directory.CreateDirectory.

But, you don't need to check if it exists first. From the documentation:

Any and all directories specified in path are created, unless they already exist or unless some part of path is invalid. If the directory already exists, this method does not create a new directory, but it returns a DirectoryInfo object for the existing directory.

How do I create directory if it doesn't exist to create a file?

To Create

(new FileInfo(filePath)).Directory.Create() before writing to the file.

....Or, if it exists, then create (else do nothing)

System.IO.FileInfo file = new System.IO.FileInfo(filePath);
file.Directory.Create(); // If the directory already exists, this method does nothing.
System.IO.File.WriteAllText(file.FullName, content);

How to create directory if it doesn't exist?

You could explicitly check whether the directory exists beforehand using isdir:

isdir(dir) || mkdir(dir)
CSV.write(joinpath(dir, "results.csv"), data)

But this will not necessarily handle all corner cases, like when the path already exists but is a link to another directory. The mkpath function in the standard library should handle everything for you:

mkpath(path)
CSV.write(joinpath(path, "results.csv"), data)

Checking folder and if it doesn't exist create it

If you want to create a folder inside a second folder or check the existence of them you can use builtin os library:

import os

PATH = 'folder_1/folder_2'
if not os.path.exists(PATH):
    os.makedirs(PATH)

os.makedirs() create all folders in the PATH if they does not exist.

Create Directory if it doesn't exist with Ruby

You are probably trying to create nested directories. Assuming foo does not exist, you will receive no such file or directory error for:

Dir.mkdir 'foo/bar'
# => Errno::ENOENT: No such file or directory - 'foo/bar'

To create nested directories at once, FileUtils is needed:

require 'fileutils'
FileUtils.mkdir_p 'foo/bar'
# => ["foo/bar"]

Edit2: you do not have to use FileUtils, you may do system call (update from @mu is too short comment):

> system 'mkdir', '-p', 'foo/bar' # worse version: system 'mkdir -p "foo/bar"'
=> true

But that seems (at least to me) as worse approach as you are using external 'tool' which may be unavailable on some systems (although I can hardly imagine system without mkdir, but who knows).

Check existence of directory and create if doesn't exist

Use showWarnings = FALSE:

dir.create(file.path(mainDir, subDir), showWarnings = FALSE)
setwd(file.path(mainDir, subDir))

dir.create() does not crash if the directory already exists, it just prints out a warning. So if you can live with seeing warnings, there is no problem with just doing this:

dir.create(file.path(mainDir, subDir))
setwd(file.path(mainDir, subDir))

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