Why file I/O is core to scripting in Bash Scripting

Introduction

File input/output (I/O) lets scripts read data from files and save results back. This helps automate tasks that involve files, like logs or reports.

You want to read a list of names from a file to process each one.

You need to save the output of a script to a file for later use.

You want to append new data to an existing log file automatically.

You need to check if a file exists before running a command.

You want to extract specific information from a file and use it in your script.

Syntax

Bash Scripting

command < input_file
command > output_file
command >> output_file

< reads input from a file instead of the keyboard.

> writes output to a file, replacing its content.

>> appends output to the end of a file.

Examples

Reads and shows the content of names.txt using input redirection.

Bash Scripting

cat < names.txt

Writes "Hello World" into greeting.txt, replacing any existing content.

Bash Scripting

echo "Hello World" > greeting.txt

Adds "New entry" at the end of log.txt without deleting existing lines.

Bash Scripting

echo "New entry" >> log.txt

Sample Program

This script reads each line from names.txt and prints a greeting. Then it writes a status message to status.txt.

Bash Scripting

#!/bin/bash

# Read names from a file and greet each
while IFS= read -r name; do
  echo "Hello, $name!"
done < names.txt

# Save a message to a file
echo "Script finished successfully." > status.txt

Important Notes

Always check if the input file exists before reading to avoid errors.

Use >> to add data without deleting existing content.

File I/O lets scripts work with real data, making automation powerful.

Summary

File I/O lets scripts read and write data to files easily.

This is useful for automating tasks that involve files, like logs or reports.

Using input/output redirection is simple and powerful in bash scripting.