CMD(3) (emu) CMD(3) NAME cmd - interface to host operating system commands SYNOPSIS bind -a '#C' / /cmd/clone /cmd/n/ctl /cmd/n/data /cmd/n/status DESCRIPTION The cmd device provides an interface to commands on the host operating system, when running emu(1). By convention, this kernel device (#C) is bound to the root directory (with the -a option). Opening the clone file provides a handle for starting a com- mand, managing the command's I/O, and checking the command's status. It creates or allocates a currently unused direc- tory, n under /cmd (where n is a decimal integer). It con- tains the files ctl, data, and status. The file descriptor returned from the open of clone provides access to the ctl file of the directory selected by cmd. Reading ctl via the file descriptor returned from opening clone provides the directory number, n, which can then be used to construct filenames for the related files. Writes to ctl must have the format: exec oscmd args ... File offset is ignored for both reading and writing. Reading data obtains the data that the command writes to its standard output and standard error. Writing to data sends the data into the command's standard input. The read-only status file provides a status line (to a maxi- mum of 128 bytes) of the format: cmd/n refcnt state cmd arg ... where each field separator is a single blank. The meaning of each field is: n The cmd directory number. refcnt The number (decimal) of open file descriptors for ctl. Page 1 Plan 9 (printed 12/21/24) CMD(3) (emu) CMD(3) state The status of the interface in directory n: Open Allocated for use but not yet running a com- mand. Execute Running a command Close Command completed. Available for reallocation via clone. cmd arg ... The active command. Output only for state Execute. Command execution On Unix systems, the command is run via /bin/sh as follows: /bin/sh -c 'cmdargs...' The command will be run using the Unix user and group ID of the user that started emu(1), unless it was started by the super-user, in which case cmd attempts to set the Unix user ID and group ID to those of a Unix user corresponding to the current Inferno user's name, and failing that, as user and group nobody. On Plan 9, the command is run via /bin/rc as follows: /bin/rc -c 'cmdargs...' The command will be run using the Plan 9 identity of the user that started emu(1). On Windows systems, the command must be a binary executable (not built into the command interpreter) in the current path. It is always run with the same Windows user identity as started emu(1). Furthermore, the ctl file transforms all slashes not quoted or escaped by backslashes to backslashes in the command string before executing it. SOURCE /emu/devcmd.c SEE ALSO emu(1), os(1) BUGS Standard output and standard error ideally should not be mingled. Exit status should be available. The maximum length of a command string is 128 bytes. Page 2 Plan 9 (printed 12/21/24)