Function

Summary

Runs an executable or shell command in a subshell.

Package

system

Signature

open-pipe command &key direction element-type interrupt-off shell-type use-pty save-exit-status => stream

Arguments

command

A string, a list of strings, a simple-vector of strings, or nil.

direction

:input, :output, :io or :none.

element-type

A type specifier.

interrupt-off

A boolean. Not implemented on Microsoft Windows.

shell-type

A shell type.

use-pty

A boolean.

save-exit-status

A boolean.

Values

stream

A pipe stream.

Description

On Unix/Linux/Mac OS X/FreeBSD the behavior of open-pipe is analogous to that of popen in the UNIX library. It creates a pipe to/from a subprocess and returns a stream. The stream can be read from or written to as appropriate.

On Microsoft Windows open-pipe calls CreateProcess and CreatePipe and returns a bidirectional stream.

command is interpreted as by call-system-showing-output.

direction is a keyword for the stream direction. The default value is :input. Bidirectional (I/O) pipes may be created by passing :io. See the example below. direction can also be :none, which means no input and no output like call-system, but is useful when you want to use pipe-exit-status and pipe-kill-process. On Windows it is not possible to open a unidirectional pipe, so :input and :output both have the same effect as :io.

When save-exit-status is non-nil, the status of the child process that open-pipe creates is tracked, so pipe-exit-status and pipe-kill-process can be used reliably. The default value of save-exit-status is nil.

element-type specifies the type of the stream as with open. The default value is base-char. This argument is ignored on Microsoft Windows.

interrupt-off, if t, ensures that Ctrl+C (SIGINT) to the LispWorks image is ignored by the subprocess. This argument is not implemented on Microsoft Windows.

shell-type specifies the type of shell to run. On Unix-like systems the default value is "/bin/sh". On Microsoft Windows the default value is "cmd". Note that on Windows ME/98/95 you will need to pass "command".

use-pty is useful on Unix-like systems if the sub-process behaves differently when running interactively and non-interactively. When use-pty is non-nil, the input and output of the sub-process are opened using PTY (Pseudo-pty). That means that the sub-process sees its input and output as if they come from an interactive terminal. The PTY also processes special characters such as Ctrl-C the same way that an ordinary TTY does.

use-pty is probably not useful on Microsoft Windows as there is no concept corresponding to the Unix behavior. If use-pty is non-nil then it uses the CREATE_NEW_PROCESS_GROUP flag when creating the child, but it is not obvious when this might be useful.

stream supports mixed character and binary I/O in the same way as file streams constructed by open.

Examples

Example on Unix:

CL-USER 1 > (setf *ls* (sys:open-pipe "ls"))

Warning: Setting unbound variable *LS*

#<SYSTEM::PIPE-STREAM "ls">

CL-USER 2 > (loop while 

                  (print (read-line *ls* nil nil)))

"hello" 

"othello" 

NIL 

NIL

CL-USER 3 > (close *ls*)

T

The following example shows you how to use bidirectional pipes.

CL-USER 1 >  (with-open-stream

                   (s (sys:open-pipe "/bin/csh"

                                     :direction :io))

                 (write-line "whereis ls" s) 

                 (force-output s)

                 (read-line s))

"ls: /sbin/ls /usr/bin/ls /usr/share/man/man1.Z/ls.1"

NIL

Example on Microsoft Windows

CL-USER 40 > (setf *ls* (sys:open-pipe "dir"))

#<WIN32::TWO-WAY-PIPE-STREAM 205F03F4>

CL-USER 41 > (loop while 

                   (print (read-line *ls* nil nil)))

" Volume in drive Z is lispsrc" 

" Volume Serial Number is 82E3-1342" 

"" 

" Directory of Z:\\v42\\delivery-tests" 

"" 

"20/02/02  11:57a        <DIR>          ." 

"20/02/02  11:57a        <DIR>          .." 

"14/02/02  07:04p             6,815,772 othello.exe" 

"14/02/02  07:07p             6,553,628 hello.exe" 

"               4 File(s)     13,369,400 bytes" 

"                          3,974,103,040 bytes free" 

NIL 

NIL

CL-USER 42 > (close *ls*)

T

This last example illustrates the use of save-exit-status. This form runs LispWorks as a subprocess such that it quits immediately with exit status 1623:

(setq *sub*

      (sys:open-pipe 

       (list (lisp-image-name)

             "-eval"

             "(quit :status 1623)") 

       :save-exit-status t))

This form then returns 1623:

(sys:pipe-exit-status *sub*)

See also

call-system
call-system-showing-output
pipe-exit-status
pipe-kill-process