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*default-pathname-defaults*

∗default-pathname-defaults∗ Variable

Value Type:

a pathname object.

Initial Value:

An implementation-dependent pathname, typically in the working directory that was current when Common Lisp was started up.

Description:

a pathname, used as the default whenever a function needs a default pathname and one is not supplied.

Examples:

;; This example illustrates a possible usage for a hypothetical Lisp running on a ;; DEC TOPS-20 file system. Since pathname conventions vary between Lisp 
;; implementations and host file system types, it is not possible to provide a ;; general-purpose, conforming example. 
\*default-pathname-defaults\* → #P"PS:<FRED>" 
(merge-pathnames (make-pathname :name "CALENDAR")) 
→ #P"PS:<FRED>CALENDAR" 
(let ((\*default-pathname-defaults\* (pathname "<MARY>"))) 
  (merge-pathnames (make-pathname :name "CALENDAR"))) 
→ #P"<MARY>CALENDAR"

Affected By:

The implementation.

Expanded Reference: *default-pathname-defaults*​

Inspecting the default pathname​

*default-pathname-defaults* holds a pathname used as the default whenever a function needs a default pathname and one is not explicitly supplied. Its initial value is implementation-dependent, typically the working directory.

(pathnamep *default-pathname-defaults*)
=> T

;; The value is implementation-dependent, e.g.:
*default-pathname-defaults*
;; => #P"/home/user/"  ; typical on Unix

Functions that use the default​

Many pathname functions such as merge-pathnames, parse-namestring, and enough-namestring use *default-pathname-defaults* when no explicit default is supplied.

;; merge-pathnames fills in from *default-pathname-defaults*
(let ((*default-pathname-defaults* #P"/home/user/projects/"))
  (merge-pathnames "report.txt"))
;; => #P"/home/user/projects/report.txt"

Temporarily binding the default​

You can use let to temporarily change the default pathname for a dynamic scope.

(let ((*default-pathname-defaults* #P"/tmp/"))
  (namestring (merge-pathnames "output.log")))
=> "/tmp/output.log"

Effect on make-pathname​

make-pathname also uses *default-pathname-defaults* to fill in the host component when no host is explicitly provided.

(let ((*default-pathname-defaults* #P"/var/data/"))
  (namestring (merge-pathnames (make-pathname :name "info" :type "txt"))))
=> "/var/data/info.txt"