Open a "process" for reading or writing. The command is executed
as a shell statement ("/bin/sh -c command
" for Unix,
"cmd /c command
" for Windows). The parameter mode
should be one of the following letters:
"r"
| Open for reading. Data written by the process to stdout
is available for read.
|
"w"
| Open for writing. Data written to the file is available
to the process on stdin.
|