Piping To/From Commands

It is often useful to be able to either write data to an external command or read data from an external command. For this there are four pipe meta-commands. All create asynchronous commands.

Two, pipe-into and pipe-from, will return a pipe handle. This is another variation on an fd handle. As you might expect, you cannot seek on a pipe handle because you can’t seek on the underlying pipe file descriptor.

The other two, named-pipe-from and named-pipe-into, will return the name of a file that can be opened for reading or writing respectively. This is the equivalent of Bash’s Process Substitution, <(...) and >(...). Most operating systems will use the /dev/fd/n-style of filename but some will use real FIFOs.

pipe variant

pipe-into.idio
oph := pipe-into nslookup

printf "oph is %s\n" oph

hprintf oph "google.com\n"

close-handle oph

;; async command last in script
(wait)
$ idio pipe-into
oph is #<H opw!   5:"/dev/fd/5":1:0>
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   google.com
Address: 216.58.212.238
Name:   google.com
Address: 2a00:1450:4009:80b::200e

Note

These examples have the asynchronous command at the end of the script meaning Idio is likely to kill it as it exits before the asynchronous command prints anything. We need a call to wait to ensure it gets a chance to run to completion.

named-pipe variant

named-pipe-into.idio
opn := named-pipe-into nslookup

printf "opn is %s\n" opn

oph := open-output-file opn

hprintf oph "google.com\n"

close-handle oph

(wait)
$ idio named-pipe-into
opn is /dev/fd/5
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   google.com
Address: 216.58.212.238
Name:   google.com
Address: 2a00:1450:4009:80b::200e

Last built at 2024-05-19T06:11:40Z+0000 from 77077af (dev) for Idio 0.3