(bash.info) Coprocesses

 
 3.2.5 Coprocesses
 -----------------
 
 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.
 
    The format for a coprocess is:
      coproc [NAME] COMMAND [REDIRECTIONS]
 
 This creates a coprocess named NAME.  If NAME is not supplied, the
 default name is COPROC.  NAME must not be supplied if COMMAND is a
 simple command ( Simple Commands); otherwise, it is interpreted
 as the first word of the simple command.
 
    When the coprocess is executed, the shell creates an array variable
 ( Arrays) named `NAME' in the context of the executing shell.
 The standard output of COMMAND is connected via a pipe to a file
 descriptor in the executing shell, and that file descriptor is assigned
 to `NAME'[0].  The standard input of COMMAND is connected via a pipe to
 a file descriptor in the executing shell, and that file descriptor is
 assigned to `NAME'[1].  This pipe is established before any
 redirections specified by the command ( Redirections).  The file
 descriptors can be utilized as arguments to shell commands and
 redirections using standard word expansions.  The file descriptors are
 not available in subshells.
 
    The process ID of the shell spawned to execute the coprocess is
 available as the value of the variable `NAME'_PID.  The `wait' builtin
 command may be used to wait for the coprocess to terminate.
 
    Since the coprocess is created as an asynchronous command, the
 `coproc' command always returns success.  The return status of a
 coprocess is the exit status of COMMAND.
Info Catalog
(bash.info) Compound Commands
(bash.info) Shell Commands
(bash.info) GNU Parallel
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