Difference between bash coproc and pipes

ychaouche · 02-10-2022, 09:04 AM

Dear LQ,

From the little I read on bash's coproc, they just seem to be serving the same
purpose as pipes, that is, giving you a means to read form a program and write
to it, the only exception here is that the communication can be bidirectionnal,
whereas in a pipe the left part only writes to the right part, and the right
part only reads from the left part.

Is there any other thing I am missing from coprocs ? can they be defined as
bidirectional pipes ?

pan64 · 02-10-2022, 09:17 AM

Quote:

A coprocess is a shell command preceded by the coproc reserved word. A coprocess is executed asynchronously in a subshell, as if the command had been terminated with the ‘&’ control operator, with a two-way pipe established between the executing shell and the coprocess.

with other words:

Quote:

coproc command in Linux is a shell command which allows us to create a co-process that is connected to the invoking shell via two pipes.

And

Quote:

A pipe is a form of redirection (transfer of standard output to some other destination) that is used in Linux and other Unix-like operating systems to send the output of one command/program/process to another command/program/process for further processing. ... You can make it do so by using the pipe character '|'.

pipe is just a redirection operator, but shell needs to create a co-proc (or two) to make it work. So yes, they are similar to each other, but not the same.

shruggy · 02-10-2022, 09:24 AM

I can see how using coprocesses may be more convenient than using named pipes and multiple redirections.

sundialsvcs · 02-10-2022, 12:01 PM

In Linux/Unix, a "pipe" appears to be a file. You can read from it or write to it. What it actually is, though, is a unidirectional queue. A process that reads from it will be blocked until data arrives. A process that writes to it will be blocked if it has become full. It can be named or anonymous.