On Thu, Mar 26, 2020 at 01:38:17PM +1100, Dave Horsfall wrote: > On Wed, 25 Mar 2020, Grant Taylor via TUHS wrote: > > > · netcat's STDOUT to grep's STDIN > > · grep's STDOUT to netcat's STDIN > > Are you trying to set up a loop of processes or something? I'm not sure if > that is even possible, although you can't rule out creative uses of dup2() > etc... This can't really be done with netcat, but it's quite easy to do with socat; here's an example with a trivial program that reads lines from its standard input and writes a single line to its standard output: [roam@straylight ~]$ socat -v tcp4:nimbus.fccf.net:25 exec:./heysmtp.py > 2020/03/28 13:09:04.005497 length=48 from=0 to=47 220 nimbus.fccf.net ESMTP Postfix (Debian/GNU)\r < 2020/03/28 13:09:04.018931 length=6 from=0 to=5 QUIT\r > 2020/03/28 13:09:04.035387 length=15 from=48 to=62 221 2.0.0 Bye\r [roam@straylight ~]$ All the output was actually from socat because of the "-v" option specified. G'luck, Peter -- Peter Pentchev roam@{ringlet.net,debian.org,FreeBSD.org} pp@storpool.com PGP key: http://people.FreeBSD.org/~roam/roam.key.asc Key fingerprint 2EE7 A7A5 17FC 124C F115 C354 651E EFB0 2527 DF13