This is a simple mini-shell that is used by foomatic-rip to execute small scripts included in some PPD files.
Some PPD files from foomatic provides small shell scripts that must be run in order to process documents sent to a printer. The script is often customized in runtime. This approach is quite flexible but also introduces security vulnerability. Originally, foomatic-rip uses default OS shell to execute the script. In ChromeOS, foomatic-rip calls foomatic_shell instead (from this package).
foomatic_shell executes given shell script in controlled environment to mitigate the security risk. It supports pipes and backticks operator (generating command by a subshell). Only very limited set of commands is allowed, foomatic_shell enforces also some restrictions on command line parameters.
When the environment variable FOOMATIC_VERIFY_MODE is set, foomatic_shell goes into no-op mode. It carries out command verification as normal but does not run the overall pipeline. For example, this environment variable is set in the printer.TestPPDs tast test..