并行运行任务
GNU parallel 可以用来同时运行多个任务：
parallel:
#!/usr/bin/env -S parallel --shebang --ungroup --jobs {{ num_cpus() }}
echo task 1 start; sleep 3; echo task 1 done
echo task 2 start; sleep 3; echo task 2 done
echo task 3 start; sleep 3; echo task 3 done
echo task 4 start; sleep 3; echo task 4 done