File existence checks in Bash Scripting

Introduction

Checking if a file exists helps your script decide what to do next, like reading a file or creating it if missing.

Before reading a file to avoid errors if the file is missing.

Before writing to a file to prevent overwriting important data.

To check if a configuration file is present before starting a program.

To verify if a backup file exists before restoring data.

To confirm if a log file is available before appending new logs.

Syntax

Bash Scripting

[ -e filename ]

Use -e to check if a file or directory exists.

Use [ ] with spaces around brackets and operators.

Examples

Checks if 'myfile.txt' exists.

Bash Scripting

[ -e myfile.txt ]

Checks if 'myfile.txt' exists and is a regular file.

Bash Scripting

[ -f myfile.txt ]

Checks if 'myfolder' exists and is a directory.

Bash Scripting

[ -d myfolder ]

Sample Program

This script checks if 'example.txt' exists in the current folder and prints a message accordingly.

Bash Scripting

#!/bin/bash

filename="example.txt"

if [ -e "$filename" ]; then
  echo "File '$filename' exists."
else
  echo "File '$filename' does not exist."
fi

Important Notes

Always put spaces around [ and ] and between operators.

Use quotes around filenames to handle spaces or special characters.

Use -f for regular files and -d for directories when you want specific checks.

Summary

Use [ -e filename ] to check if a file or directory exists.

Use if-else to run different commands based on file existence.

Quotes around filenames help avoid errors with spaces.