Unix in a Nutshell, 4th Edition

Coprocesses

Coprocesses are a feature of the Korn shell only.

cmd1 | cmd2 |&	Coprocess; execute the pipeline in the background. The shell sets up a two-way pipe, allowing redirection of both standard input and standard output.
read -p var	Read coprocess output into variable var.
print -p string	Write string to the coprocess.
cmd <&p	Take input for cmd from the coprocess.
cmd >&p	Send output of cmd to the coprocess.
exec n <&p	Move input from coprocess to file descriptor n.
exec n >&p	Move output for coprocess to file descriptor n.

Moving the coprocess input and output file descriptors to standard file descriptors allows you to open multiple coprocesses .

Examples

    $ ed - memo |&           
                     Start coprocess
    $ print -p /word/        
                     Send ed command to coprocess
    $ read -p search         
                     Read output of ed command into variable search
    $ print "$search"        
                     Show the line on standard output
    A word to the wise.