I thought that make interprets the rule's set of commands literally, passing them to the sub-shell. But this doesn't seem to work in this case:
default: loop
echo $$RANDOM
This prints echo $RANDOM in my shell but doesn't actually print the number.
GNU make: Choosing the shell says that the default shell is /bin/sh.
$RANDOM is a bash feature, so you could explicitly tell make to use bash by putting
SHELL := '/bin/bash'
at the top of your Makefile.
(echo $RANDOM is just make echoing the command it's going to run.)
