Check out mkdir; specifically the -p option.

You can see if a directory exists with -d.  This tells you with a single command whether the specified path exists, and is a directory.  Of course, you would also presumably need to use -f to make sure a file with the same name does NOT exist:

# Assuming $path contains the full pathname of the file/directory
if (-d $path) {
    # It's an existing directory
} elsif (-f $path) {
    # It's an existing file
}
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