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bash Pocket Reference
book

bash Pocket Reference

by Arnold Robbins
May 2010
Beginner to intermediate content levelBeginner to intermediate
130 pages
3h 20m
English
O'Reilly Media, Inc.
Content preview from bash Pocket Reference

Coprocesses

A coprocess is a process that runs in parallel with the shell and with which the shell can communicate. The shell starts the process in the background, connecting its standard input and output to a two-way pipe. There are two syntaxes for running a coprocess:

    coproc name non-simple command  Start a named coprocess

    coproc command args             Start an unnamed coprocess

The shell creates an array variable named name to hold the file descriptors for communication with the coprocess. name[0] is the output of the coprocess (input to the controlling shell) and name[1] is the input to the coprocess (output from the shell). In addition, the variable name_PID holds the process-ID of the coprocess. When no name is supplied, the shell uses COPROC.

Caution

As of version 4.1, there can be only one active coprocess at a time.

Example

The following example demonstrates the basic usage of the coproc keyword and the related variables:

$ coproc testproc (echo 1          Start a named coprocess
> read aline ; echo $aline)        in the background
[1] 5090
$ echo ${testproc[@]}              Show the file descriptors
63 60
$ echo $testproc_PID               Show the coprocess PID
5090
$ read out <&${testproc[0]}        Read the first line of coprocess
$ echo $out                        output and show it
1
$ echo foo >&${testproc[1]}        Send coprocess some input
$ read out2 <&${testproc[0]}       Read second output line
[1]+ Done  coproc testproc (echo 1; read aline; echo $aline)
$ echo $out2                       Show the second output line
foo
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Publisher Resources

ISBN: 9781449388669Errata Page