+# -) an array of arrays
+# Each array represents a command, and each command's output is piped into
+# the following command's standard input.
+# For this a shell command string is created with pipe symbols between each
+# command.
+# Each command is a list of strings meant to end up in the final command
+# unchanged. In order to achieve this, every argument is shell-quoted.
+# Quoting can be disabled for a particular argument by turning it into a
+# reference, this allows inserting arbitrary shell options.
+# For instance: the $cmd [ [ 'echo', 'hello', \'>/dev/null' ] ] will not
+# produce any output, while the $cmd [ [ 'echo', 'hello', '>/dev/null' ] ]
+# will literally print: hello >/dev/null