Command not found in Bash's IF-ELSE condition when using [! -d “$DIR”]

Question

I have a code like this

#!/bin/bash 
DIR=\"test_dir/\";
if [! -d \"$DIR\"]; then
    # If it doesn\'t create it
    mkdir $DIR
fi

But why

Answer 1

Add some spaces:

if [ ! -d "$DIR" ]; then
#   ^           ^

Answer 2

Add space between [ and !. And before ] as well.

#!/bin/bash 
DIR="test_dir/";
if [ ! -d "$DIR" ]; then
    # If it doesn't create it
    mkdir $DIR
fi

It's also a good idea to quote your variable:

    mkdir "$DIR"

Answer 3

You could also attempt to simply by saying:

test -d "${dir}" || mkdir "${dir}"

This would create the directory if it doesn't exist.