Using while loops with read

If you want to loop over values in a file, the read command in Linux/Unix is very useful. It reads a line from a file, and assigns as many variables as you specify as parameters to the values in that line. Combined with a while loop, you can read the values and process them. Here’s an example :

while read customernr
do
  <some_script> $customernr
done < customers.txt

This loops over all the lines in the customers.txt file. This file contains one customer number per line. Then we can reference this customer number as $customernr, and process it. Here that value is given as a parameter to some script.

Thanks to Steve Parker’s website for reminding me of the syntax of the while loop. It’s funny how Google has replaced reading man pages.