Here’s a simple shell trick that does a loop through some numbers:
for i in {0..10}; do echo $i; done
For example, sometimes you want to test some concurrent read/write performance on database or whatever, you can do:
for i in {1..10}; do (echo $i; ./read_db.sh $i &); done
This will generate 10 processes that execute the read_db.sh script concurrently.