temporary-directory

Arguments:

Returns the pathname of the temporary directory used by the current running Lisp for writing temporary files and sets, if necessary, the value of sys:*temporary-directory* to that directory.

This function works as follows:

1. The value of sys:*temporary-directory* is examined. If its value is nil, a new temporary directory is selected using the algorithm below.
2. The value of (probe-file sys:*temporary-directory*) is examined. If it is true, the value of sys:*temporary-directory* is returned. If the value returned by probe-file is nil, then a new temporary directory is selected using the algorithm below.

In a freshly installed Lisp image, the initial value of sys:*temporary-directory* is nil. However, in a user-built image (made with dumplisp or build-lisp-image or generate-application), sys:*temporary-directory* may have been given a value, which might or might not be a valid value on the machine where the image is run. If it is not a valid value, the behavior is the same as when the value is nil. But it can happen (perhaps unexpectedly) that the value is valid and in that case it is used.

Algorithm for choosing a temporary directory

If a temporary directory must be chosen, it is chosen according to the following algorithms.

On UNIX and the Mac: #p"/tmp/".

On Windows: the first of the following to be a valid directory is used:

• the value of the environment variable TEMP
• the value of the environment variable TMP
• [current-drive]:\tmp
• C:\ (the last presumably always exists)

When a directory is chosen by this algorithm, the value of sys:*temporary-directory* is set to it.

This function does not work with setf. It is informational only. You can change the temporary directory by changing the value of sys:*temporary-directory* to the desired directory pathname. Whenever this function is called, it tests whether (probe-file sys:*temporary-directory*) returns true, returning the value of sys:*temporary-directory* when it is. If (probe-file sys:*temporary-directory*) returns nil, a new value is chosen using the algorithm above. Changing the temporary directory is not recommended.

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This page was not revised from the 8.2 page.
Created 2012.5.30.