How to check if a directory exists or not in a Bash shell script

In a Bash shell script, you can check if a directory exists by using the -d flag with an if statement. The -d flag returns true if the specified directory exists. For example, you can write if [ -d "/path/to/directory" ]; then echo "Directory exists"; else echo "Directory does not exist"; fi. This simple construct allows you to conditionally execute code based on the presence of a directory, which can be useful in scripts that need to verify the existence of directories before proceeding with file operations or other tasks.

Explanation and Examples

Basic Directory Check:
Using the -d flag is straightforward. Here’s a breakdown of the command:

if [ -d "/path/to/directory" ]; then
    echo "Directory exists"
else
    echo "Directory does not exist"
fi

• [ -d "/path/to/directory" ]: This condition checks if the directory exists.
• then: If the directory exists, the commands following then are executed.
• else: If the directory does not exist, the commands following else are executed.
• fi: This marks the end of the if statement.

Practical Example:
Let’s consider a script that backs up data only if a specific directory exists:

#!/bin/bash

BACKUP_DIR="/backup/data"

if [ -d "$BACKUP_DIR" ]; then
    echo "Backup directory exists. Proceeding with backup..."
    # Your backup commands here
else
    echo "Backup directory does not exist. Aborting backup."
fi

This script checks for the existence of /backup/data. If the directory is present, it proceeds with the backup process; otherwise, it aborts.

Advanced Use Cases

Creating a Directory if it Doesn’t Exist:
Sometimes you may want to create a directory if it doesn’t exist:

TARGET_DIR="/new/directory"

if [ ! -d "$TARGET_DIR" ]; then
    echo "Directory does not exist. Creating directory..."
    mkdir -p "$TARGET_DIR"
else
    echo "Directory already exists."
fi

• if [ ! -d "$TARGET_DIR" ]; then: The ! operator negates the condition, checking if the directory does not exist.
• mkdir -p "$TARGET_DIR": This command creates the directory, including any necessary parent directories.

Checking Multiple Directories:
If you need to check multiple directories, you can use a loop:

for DIR in "/path/one" "/path/two" "/path/three"; do
    if [ -d "$DIR" ]; then
        echo "Directory $DIR exists."
    else
        echo "Directory $DIR does not exist."
    fi
done

This script iterates over a list of directories and checks each one.

Best Practices

Quoting Variables:
Always quote your variables to prevent issues with spaces or special characters:

if [ -d "$MY_DIRECTORY" ]; then
    echo "Directory exists."
fi

Using -e for Files and Directories:
If you need to check for both files and directories, use the -e flag:

if [ -e "$FILE_OR_DIR" ]; then
    echo "File or directory exists."
fi

This is less specific but useful in certain scenarios.

Error Handling:
Incorporate error handling to manage unexpected situations gracefully:

if [ -d "$MY_DIR" ]; then
    echo "Directory exists."
else
    echo "Error: Directory does not exist." >&2
    exit 1
fi

Redirecting errors to stderr using >&2 and exiting with a non-zero status code is a good practice.

Summary

Checking for the existence of a directory in Bash is a fundamental task that can be handled easily with the -d flag in an if statement. By understanding and applying this basic construct, you can build more complex and robust scripts that perform necessary checks before proceeding with operations. Whether you need to create directories, verify multiple paths, or handle errors effectively, mastering this technique is essential for efficient Bash scripting.