how to loop a .sh file on linux code example

Example 1: bash loop over files in directory

#!/bin/bash
for filename in /Data/*.txt; do
    ...
done

Example 2: loop bash

years=(2018 2019)
days=(74 274)

for year in "${years[@]}"; do
    for day in $(seq -w ${days[0]} ${days[1]}); do
               echo $year
               echo $day
    done
done