Bash Co-Processes

"One of the new features in bash 4.0 is the coproc statement. The coproc statement allows you to create a co-process that is connected to the invoking shell via two pipes: one to send input to the co-process and one to get output from the co-process.

"The first use that I found for this I discovered while trying to do logging and using exec redirections. The goal was to allow you to optionally start writing all of a script's output to a log file once the script had already begun (e.g. due to a --log command line option).

"The main problem with logging output after the script has already started is that the script may have been invoked with the output already redirected (to a file or to a pipe). If we change where the output goes when the output has already been redirected then we will not be executing the command as intended by the user."

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