You’re looking for the isdirectory() function:
isdirectory({directory}) *isdirectory()* The result is a Number, which is non-zero when a directory with the name {directory} exists. If {directory} doesn't exist, or isn't a directory, the result is FALSE. {directory} is any expression, which is used as a String.
Unlike filereadable(), this function doesn’t check whether the directory is readable; it only checks whether it exists. (Correspondingly, there isn’t a single built-in function to check whether a file exists without also checking that it’s readable. This answer demonstrates how to use the glob() function to do this kind of check.)
To summarize,
To check whether a file or directory named name exists,
!empty(glob(name))
To check whether a file (not a directory) named file_name exists,
!empty(glob(file_name)) && !isdirectory(file_name)
To check whether a directory (not a file) named dir_name exists,
isdirectory(dir_name)
To check whether a file (not a directory) named file_name exists and is readable,
filereadable(file_name)
I’m not sure how to check whether a directory (not a file) of a specified name exists and is readable.
For the forms that use glob(), don’t forget that certain characters like * are special and need to be escaped if they occur literally in the filename. See :help wildcard for more information.
