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.

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 remrem.md 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