That's what the extra :s in ":$PATH:" are for: they prepend and append an empty component to the list. Any component in the original "$PATH" will still be in ":

That's what the extra :s in ":$PATH:" are for: they prepend and append an empty component to the list. Any component in the original "$PATH" will still be in ":$PATH:" too, but no longer be at the end or the beginning, allowing the pattern to be simplified.