Sub-process Execution

The exec node-type spawns a new subprocess and exchanges sample data via stdin and stdout.

Prerequisites

This node-type does not have any special library dependencies. It is always available.

Implementation

The source code of the node-type is available here: https://git.rwth-aachen.de/acs/public/villas/node/blob/master/lib/nodes/exec.cpp

Configuration

format (string: format-id) = "villas.human"

A IO format identifier selecting the file format which is used for reading and writing from the file.

See Format-types for a complete list of supported formats.

shell (boolean) = false

If set, the -config-node-exec-exec setting gets passed the shell (/usr/bin). In this case the exec setting must be given as a string.

If not set, we will directly execute the sub-process via execvpe(2). In this case the exec setting must be given as an array (argv[]).

exec (string|array)

The program which should be execed in the sub-process.

The options is passed to the system shell for execution.

flush (boolean) = true

Flush stream every time VILLASnode passes data the sub-process.

working_directory (string: path)

If set, the working directory for the sub-process will be changed.

environment (object)

A object of key/value pairs of environemnt variables which should be passed to the sub-process in addition to the parent environment.

Example

nodes = {
        exec_node = {
                type = "exec"
                format = "villas.human"
                flush = true
                exec = "tee test"
                shell = true
                working_directory = "/tmp"
                environment = {
                        MYVAR = "TESTVAL"
                }
        }
}