Subversion Repositories SvarDOS

=== PIPING COMMANDS ==========================================================

Piping a command means redirecting its standard output (stdout) to the

standard input (stdin) of another command. While redirection of file handles

is a concept well supported by the DOS kernels, piping is not, in part due to

the mono-task nature of DOS. SvarCOM provides piping support through following

logic:

1. user-entered (or batch-acquired) command line is analyzed for any kind of

   redirections (incl. pipes) by redir_parsecmd(). If the command appears to

   be piped, then redir_parsecmd() enforces a stdout redirection to a

   temporary file and moves all the pipe chain to an RMOD-owned buffer named

   "awaitingcmd", appending an stdin redirection so the next command's stdin

   is fed from the temporary file. The command is then executed.

2. before further execution, SvarCOM looks into its "awaitingcmd" buffer, and

   if it is non-empty, it runs its content.

3. when loading commands from the awaitingcmd, SvarCOM sets a special

   "delete_stdin_file" flag and passes it to command-executing functions so

   these remember to delete the stdin-redirected file.