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Common Lisp
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===Find the list of available shells=== WITH-OPEN-FILE is a macro that opens a file and provides a stream. When the form is returning, the file is automatically closed. FUNCALL calls a function object. The LOOP collects all lines that match the predicate. <syntaxhighlight lang="lisp"> (defun list-matching-lines (file predicate) "Returns a list of lines in file, for which the predicate applied to the line returns T." (with-open-file (stream file) (loop for line = (read-line stream nil nil) while line when (funcall predicate line) collect it))) </syntaxhighlight> The function AVAILABLE-SHELLS calls the above function LIST-MATCHING-LINES with a pathname and an anonymous function as the predicate. The predicate returns the pathname of a shell or NIL (if the string is not the filename of a shell). <syntaxhighlight lang="lisp"> (defun available-shells (&optional (file #p"/etc/shells")) (list-matching-lines file (lambda (line) (and (plusp (length line)) (char= (char line 0) #\/) (pathname (string-right-trim '(#\space #\tab) line)))))) </syntaxhighlight> Example results (on Mac OS X 10.6): <syntaxhighlight lang="lisp"> CL-USER > (available-shells) (#P"/bin/bash" #P"/bin/csh" #P"/bin/ksh" #P"/bin/sh" #P"/bin/tcsh" #P"/bin/zsh") </syntaxhighlight>
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