OUTPUT-TO-FILE.html -- ACL2 Version 6.3

## OUTPUT-TO-FILE

redirecting output to a file

    Major Section:  IO

For a general discussion of ACL2 input/output and of the ACL2 read-eval-print loop, see io and see ld (respectively). Here we use an example to illustrate how to use some of the options provided by `ld` to redirect ACL2 output to a file, other than the printing of the prompt (which continues to go to the terminal).

There are two `ld` specials that control output from the `ld` command: `proofs-co` for proof output and `standard-co` for other output. The following example shows how to use these to redirect output to a file `"tmp.out"`. The following command opens a character output channel to to the file `"tmp.out"` and redirects proof output to that channel, i.e., to file `"tmp.out"`.

    (mv-let (chan state)
            (open-output-channel "tmp.out" :character state)
            (set-proofs-co chan state))

Next, we redirect standard output to that same channel.

    (set-standard-co (proofs-co state) state)

Now we can load an input file, in this case file `"tmp.lisp"`, and output will be redirected to file `"tmp.out"`. (The use of `:ld-pre-eval-print t` is optional; see ld.)

    (ld "tmp.lisp" :ld-pre-eval-print t)

Having completed our load operation, we restore both proof output and standard output to the terminal, as follows.

    (set-standard-co *standard-co* state)
    (close-output-channel (proofs-co state) state)
    (set-proofs-co *standard-co* state)

The following variant of the above example shows how to redirect output as above except without changing the global settings of the two `ld` specials, `proofs-co` and `standard-co`. This approach uses a notion of ``global variables'' stored in the ACL2 state; see assign and see @.

    (mv-let (chan state)
            (open-output-channel "tmp.out" :character state)
            (assign tmp-channel chan))
    (ld "tmp.lisp" :ld-pre-eval-print t
                   :proofs-co (@ tmp-channel)
                   :standard-co (@ tmp-channel))
    (close-output-channel (@ tmp-channel) state)