Shellbox command validation component.
Implementation work on a parser for UNIX shell commands is underway. The concept is to extract a feature flag list (pipelines, variable expansion, subshells, etc.) and a list of literal arguments.
Configuration will specify a whitelist of allowed features. Arguments may be specified to be either a fixed string literal or a valid relative path.
Relative paths are expected as command-line arguments in Shellbox since input and output files are placed in an otherwise empty working directory.