Gforth can be used in pipes created elsewhere (described in the following). It can also create pipes on its own (see Pipes).
If you pipe into Gforth, your program should read with read-file
or read-line from stdin (see General files).
Key does not recognize the end of input. Words like
accept echo the input and are therefore usually not useful for
reading from a pipe. You have to invoke the Forth program with an OS
command-line option, as you have no chance to use the Forth command line
(the text interpreter would try to interpret the pipe input).
You can output to a pipe with type, emit, cr etc.
When you write to a pipe that has been closed at the other end, Gforth
receives a SIGPIPE signal (“pipe broken”). Gforth translates this
into the exception broken-pipe-error. If your application does
not catch that exception, the system catches it and exits, usually
silently (unless you were working on the Forth command line; then it
prints an error message and exits). This is usually the desired
behaviour.
If you do not like this behaviour, you have to catch the exception yourself, and react to it.
Here’s an example of an invocation of Gforth that is usable in a pipe:
gforth -e ": foo begin pad dup 10 stdin read-file throw dup while \ type repeat ; foo bye"
This example just copies the input verbatim to the output. A very simple pipe containing this example looks like this:
cat startup.fs | gforth -e ": foo begin pad dup 80 stdin read-file throw dup while \ type repeat ; foo bye"| head
Pipes involving Gforth’s stderr output do not work.