CMD(3)                                                     CMD(3)

          cmd - interface to host operating system commands

          bind -a '#C' /


          Cmd provides a way to run commands in the underlying operat-
          ing system's command interpreter of drawterm or when Inferno
          is running hosted.  It serves a three-level directory that
          is conventionally bound behind the root directory.  The top
          of the hierarchy is a directory cmd, that contains a clone
          file and zero or more numbered directories.  Each directory
          represents a distinct connection to the host's command
          interpreter.  The directory contains five files: ctl, data,
          stderr, status and wait, used as described below.  Opening
          the clone file reserves a connection: it is equivalent to
          opening the ctl file of an unused connection directory, cre-
          ating a new one if necessary.

          The file ctl controls a connection.  When read, it returns
          the decimal number n of its connection directory.  Thus,
          opening and reading clone allocates a connection directory
          and reveals the number of the allocated directory, allowing
          the other files to be named (eg, /cmd/n/data).

          Ctl accepts the following textual commands, allowing quoting
          as interpreted by parsecmd(2):

          dir wdir
               Run the host command in directory wdir, which is a
               directory on the host system . Issue this request
               before starting the command.  By default, commands are
               run in the Inferno root directory on the host system.

          exec command args ...
               Spawn a host process to run the command with arguments
               as given.  The write returns with an error, setting the
               error string, if anything prevents starting the com-
               mand.  If write returns successfully, the command has
               started, and its standard input and output may be
               accessed through data, and its error output accessed
               through stderr (see below).  If arguments containing

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     CMD(3)                                                     CMD(3)

               white space are quoted (following the conventions of
               rc(1) or parsecmd(2)), they are requoted by cmd using
               the host command interpreter's conventions so that
               command sees exactly the same arguments as were written
               to ctl.

          kill Kill the host command immediately.

               Set the device to kill the host command when the ctl
               file is closed (normally all files must be closed, see

          nice [n]
               Run the host command at less than normal scheduling
               priority.  Issue this request before starting the com-
               mand.  The optional value n, in the range 1 to 3, indi-
               cates the degree of `niceness' (default: 1).

          The data file provides a connection to the input and output
          of a previously-started host command.  It must be opened
          separately for reading and for writing.  When opened for
          reading, it returns data that the command writes to its
          standard output; when closed, further writes by the command
          will receive the host equivalent of `write to closed pipe'.
          When opened for writing, data written to the file can be
          read by the command on its standard input; when closed, fur-
          ther reads by the command will see the host equivalent of
          `end of file'.  (Unfortunately there is no way to know when
          the command needs input.)

          The stderr file provides a similar read-only connection to
          the error output from the command.  If the stderr file is
          not opened, the error output will be discarded.

          Once started, a host command runs until it terminates or
          until it is killed, by using the kill or killonclose
          requests above, or by closing all ctl, data and wait files
          for a connection.

          The read-only status file provides a single line giving the
          status of the connection (not the command), of the form:

               cmd/n opens state wdir arg0

          where the fields are separated by white space. The meaning
          of each field is:

          n    The cmd directory number.

               The decimal number of open file descriptors for ctl,

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     CMD(3)                                                     CMD(3)

               data and wait.

               The status of the interface in directory n:

               Open     Allocated for use but not yet running a com-
               Execute  Running a command.
               Done     Command terminated: status available in the
                        status file (or via wait).
               Closed   Command completed. Available for reallocation
                        via clone.

          wdir The command's initial working directory on the host.

          arg0 The host command name (without arguments).

          The read-only wait file must be opened before starting a
          command via ctl.  When read, it blocks until the command
          terminates.  The read then returns with a single status
          line, to be parsed using tokenize (see getfields(2)). There
          are five fields: host process ID (or 0 if unknown); time the
          command spent in user code in milliseconds (or 0); time
          spent in system code in milliseconds (or 0); real time in
          milliseconds (or 0); and a string giving the exit status of
          the command.  The exit status is host-dependent, except that
          an empty string means success, and a non-empty string con-
          tains a diagnostic.

        Command execution
          In all cases, the command runs in the host operating
          system's own file name space.  All file names will be inter-
          preted in that space, not Plan9's.  For example, on Unix /
          refers to the host's file system root, not Plan9's; the
          effects of mounts and binds will not be visible.


          A write to ctl returns with an error and sets the error
          string if a command cannot be started or killed success-

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