Writing to files (echo, printf) in Bash Scripting

Introduction

Writing to files lets you save information from your script so you can use it later or share it.

Save a list of names or data generated by a script.

Create a log file to keep track of what your script did.

Store user input or results for later review.

Generate configuration files automatically.

Backup important information before making changes.

Syntax

Bash Scripting

echo "text" > filename
printf "format" > filename

echo adds a newline automatically at the end.

printf gives more control over formatting but needs explicit newlines.

Examples

This writes "Hello World" into file.txt, replacing any existing content.

Bash Scripting

echo "Hello World" > file.txt

This adds "Line 1" to the end of file.txt without removing existing content.

Bash Scripting

echo "Line 1" >> file.txt

This writes formatted text with a name and age into info.txt.

Bash Scripting

printf "Name: %s\nAge: %d\n" "Alice" 30 > info.txt

Sample Program

This script writes three lines to output.txt. It first writes a start message, then adds user info with printf, and finally adds a finish message. The cat command shows the file content.

Bash Scripting

#!/bin/bash

echo "Starting the script..." > output.txt
printf "User: %s\nScore: %d\n" "Bob" 85 >> output.txt
echo "Script finished." >> output.txt

cat output.txt

Important Notes

Use >> to add to a file without erasing it.

Remember to give your script permission to write to the file location.

Use quotes around text to avoid problems with spaces or special characters.

Summary

Use echo or printf to write text to files in bash.

echo is simple and adds a newline automatically.

printf is more flexible for formatting but needs explicit newlines.