Should a directory path variable end with a trailing slash?

I go with the trailing slash because:

1. “If it ends with a slash, it’s a directory. If not, it’s a file.” is an easy convention to remember.

2. At least on the operating systems I commonly use, doubling the slash causes no problems, while omitting the slash causes big ones. It is, therefore, safest to both put the slash into the variable and use "$path/$file" when making use of it.