Use the brace expansion mechanism of Bash, multiple sub project tasks can be run in the command line like below.
$ ./gradlew sub-prj-1:{tasks,help}
After brace expansion, it is same as below, but saves some typing.
$ ./gradlew sub-prj-1:tasks sub-prj-1:help
More examples.
$ ./gradlew sub-prj-{1,2}:test
# same as
# ./gradlew sub-prj-1:test sub-prj-2:test
$ ./gradlew sub-prj-{1,2}:{clean,build}
# same as
# ./gradlew sub-prj-1:clean sub-prj-1:build sub-prj-2:clean sub-prj-2:build