How to Process a File Line-by-Line in Bash

The aim of this page is to explain shell scripting concepts related to IFS (Internal Field Separator) based on the particular example of using IFS within a while loop to process lines from a file, even without curly braces. I have a file full of the URL paths to Hashicorp’s Consul Keys that I need to open in a browser and manually modify.

Pavol Kutaj
2 min readMay 30, 2024
  • IFS is a special shell variable that defines the characters used to separate words (fields) when splitting a line of text.
  • The default value of IFS includes whitespace characters like space, tab, and newline.
  • In the provided code lines in file are values for the cui command (irrelevant here)
  • Then, I stop for 10 seconds to check the results and press enter to continue (cui keeps opening URLs in a browser, irrelevant here)
while IFS= read -r line; do
cui $line
echo "pause..."
read -t 10 < /dev/tty
done < cui_input_values.txt
  • IFS= sets IFS to an empty string, preventing unintended word splitting within the loop's command.
  • read -r line reads a line from the file and assigns it to the variable line.
  • It’s recommended to reset IFS back to its default value after the loop or use a temporary variable to store and restore its original value.
  • The code snippet IFS= read -r line forms a single statement within the while loop.
  • IFS= is an assignment that modifies the environment for the read command that follows.
  • The newline acts as a command separator when the code is not part of a control structure like a loop.
  • The input redirection < cui_input_values.txt passes a file — containing a list of URLs — into the loop that keeps opening them in a browser




Pavol Kutaj

Today I Learnt | Infrastructure Support Engineer at with a passion for cloud infrastructure/terraform/python/docs. More at