Making a system call that returns the stdout output as a string

Question

Perl and PHP do this with backticks. For example,

$output = `ls`;

Returns a directory listing. A similar function, system(\"foo\")

Answer 1

Here's another Lisp way:

(defun execute (program parameters &optional (buffer-size 1000))
  (let ((proc (sb-ext:run-program program parameters :search t :output :stream))
        (output (make-array buffer-size :adjustable t :fill-pointer t 
                            :element-type 'character)))
    (with-open-stream (stream (sb-ext:process-output proc))
      (setf (fill-pointer output) (read-sequence output stream)))
    output))

Then, to get your string:

(execute "cat" '("/etc/hosts"))

If you want to run a command that creates prints a great deal of info to STDOUT, you can run it like this:

(execute "big-writer" '("some" "parameters") 1000000)

The last parameter preallocates a large amount of space for the output from big-writer. I'm guessing this function could be faster than reading the output stream one line at a time.