Working with Files and Directories: Part 3

Part 3: Working with Files and Directories

Welcome back to our “Mastering Bash Scripting for Embedded Linux Development“ series! In this third part, we’ll explore essential techniques for working with files and directories in Bash scripting. From file manipulation to directory traversal and pattern matching, mastering these concepts will empower you to efficiently manage and manipulate data within your embedded Linux systems.

File Manipulation

Bash scripting provides powerful tools for manipulating files, including creating, reading, writing, and deleting them.

Directory Traversal

Navigating directories and accessing files within them is a common task in Bash scripting. You can use commands like cd, ls, and pwd to traverse directories and perform operations on files.

Changing Directories

Use the cd command followed by the directory name to change your current working directory. For example,

# Change directory
cd /path/to/directory

Listing Contents

The ls command lists the contents of a directory. Adding options such as -l provides detailed information about files, including permissions and ownership.

# List files in the current directory
ls

# Print the current directory
pwd

Moving Files

You can move files between directories using mv. For instance, to move file.txt from the current directory to Documents:

mv file.txt Documents/

Copying Files

Similarly, copy files with cp. For example, to copy file.txt to a backup folder:

cp file.txt backup/

File Permissions and Ownership

Understanding file permissions and ownership is crucial for securing your files and controlling access. In Linux systems, each file has permissions for the owner, group, and others, denoted by read (r), write (w), and execute (x).

• Viewing Permissions: Utilize the ls -l command to view permissions. Permissions are displayed as a sequence of characters, such as -rwxr-xr--, where the first three characters represent permissions for the owner, the next three for the group, and the last three for others.
• Changing Permissions: The chmod command allows you to change file permissions. Syntax: chmod [permissions] filename. For instance, chmod +x script.sh adds execute permissions to script.sh.
• Ownership: The chown command changes the ownership of files. Syntax: chown [user]:[group] filename. For example, chown user:group example.txt changes the ownership of example.txt.

To modify file permissions using octal notation, you would use the chmod command followed by the octal representation of the desired permissions. For example:

# Change file permissions
chmod 755 script.sh

Bash Scripting

Example 1: Create 10 Files with Random String

#!/bin/bash

# This script creates 10 files with random strings as their content

# Define files to create
files=("file1.txt" "file2.txt" "file3.txt" "file4.txt" "file5.txt"
       "file6.txt" "file7.txt" "file8.txt" "file9.txt" "file10.txt")

# Create files with random content
for file in "${files[@]}"; do
    # Generate a random string
    random_string=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1)
    echo "$random_string" > "$file"
done

echo "Files created successfully!"

Example 2: Automated File Backup Script

#!/bin/bash

# This script creates a backup of specified files

# Define files to backup
files="file1.txt file2.txt"

# Create a backup directory if it doesn't exist
backup_dir="backup"
if [ ! -d "$backup_dir" ]; then
    mkdir "$backup_dir"
fi

# Copy files to the backup directory
for file in $files; do
    cp "$file" "$backup_dir/"
done

echo "Backup completed successfully!"

Example 3: File Permission Checker

#!/bin/bash

# This script checks the permissions of a file

# Define file to check
file="file1.txt"

# Check file permissions
permissions=$(ls -l "$file" | cut -d ' ' -f 1)

echo "Permissions of $file: $permissions"

Bash Scripting

Example 4: Pattern Matching Script

#!/bin/bash

# This script lists all text files in the current directory

# List text files
echo "Text files:"
ls *.txt

Example 5: File Cleanup Script

#!/bin/bash

# This script deletes all text files in the current directory

# Delete all text files
find . -name "*.txt" -type f -delete

echo "Text files deleted successfully!"

In this part of our series, we’ve explored essential techniques for working with files and directories in Bash scripting. From file manipulation to directory traversal and pattern matching, these concepts are foundational for managing data within your embedded Linux systems.

Q: Can I create a file and a directory with the same name?
A: No, a file and a directory cannot share the same name in the same location. However, they can have the same name if they are in different locations.

Q: How can I view the contents of a file without using cat, less, or more?
A: You can use the head command to display the first part of a file, or the tail command to display the last part of a file.

Q: What is the difference between > and >>?
A: The > operator overwrites the file with the output of the command, while the >> operator appends the output to the end of the file.

Q: How can I delete a directory that is not empty?
A: You can use the rm -r command to remove a directory and its contents. Be careful with this command, as it will delete the directory and all of its contents without asking for confirmation.

For more detailed information, you can always refer to the official GNU Bash documentation.

That’s all for today’s post.

Stay curious, keep exploring, and happy scripting!

This concludes Part 3 of our series. Stay tuned for future installments!