merge-pathnames

(merge-pathnames pathname &optional defaults)

Fills the gaps in pathname from defaults and returns the merged pathname. Both arguments take either spelling (a pathname or a namestring), and the rule works on the two parts a namestring has: the directory (everything through the last /) and the file (what follows it). The directory of pathname wins when it is absolute, is appended to defaults' directory when it is relative, and is taken from defaults when pathname has none; the file of pathname wins unless it is empty. Omitting defaults merges against the working directory, which leaves pathname unchanged.

This is how a library names a file relative to a directory it computed earlier -- a data file next to its own sources, say. uiop:merge-pathnames* is the ASDF/UIOP spelling of the same merge.

Backend support

Works on all four backends: one definition in rontolisp source, spliced into the program when it is referenced.