Bash foreach Directory Loop - Shell-Bash

Bash provides a foreach loop to iterate over directories and perform various actions on each directory or its contents. In this guide, we will explore how to use the foreach loop in the Bash shell script to programmatically process multiple directories.

Syntax

The basic syntax of the foreach loop in Bash is as follows:

for dir in /path/to/dir/*; do
    # Statements to execute for each directory
    echo "Processing ${dir}" 
    # ...
done

In this syntax, /path/to/dir/* represents the source directory or pattern to match directories. You can specify a specific directory path or use wildcards to match multiple directories.

Example: Counting Files in Directories

Let's take a simple example to count the number of files in each directory using the foreach loop. Consider the following script:

#!/bin/bash

for dir in /path/to/dir/*; do
    if [ -d "${dir}" ]; then
        file_count=$(ls -l "${dir}" | grep -v "^d" | wc -l)
        echo "Directory ${dir} contains ${file_count} files."
    fi
done

Explanation:

• The if [ -d "${dir}" ] condition checks if the iteration value ($dir) is a directory.
• ls -l "${dir}" lists the files and directories within "${dir}".
• grep -v "^d" filters out the lines that start with 'd' (directories).
• wc -l counts the number of lines (files).
• The echo statement prints the directory path and the number of files it contains.

Make sure to replace /path/to/dir/* with the actual directory path or pattern you want to process.

Example: Renaming Files in Directories

Let's explore another example to rename all the files within multiple directories using the foreach loop. Here's an example script:

#!/bin/bash

for dir in /path/to/dir/*; do
    if [ -d "${dir}" ]; then
        for file in "${dir}"/*; do
            if [ -f "${file}" ]; then
                new_name="${file}.bak"
                mv "${file}" "${new_name}"
                echo "Renamed ${file} to ${new_name}."
            fi
        done
    fi
done

Explanation:

• Similar to the previous example, the if [ -d "${dir}" ] checks if the iteration value ($dir) is a directory.
• The nested for file in "${dir}"/* loop iterates over each file within the current directory.
• The if [ -f "${file}" ] condition verifies if the iteration value ($file) is a regular file.
• The new_name="${file}.bak" line creates a new name for the file by appending .bak extension.
• mv "${file}" "${new_name}" renames the file.
• The echo statement prints the original file name and the new renamed file.

Again, replace /path/to/dir/* with the actual directory path.

Conclusion

The Bash foreach directory loop provides a flexible and powerful way to process multiple directories and their contents. You can modify the loop statements to perform various tasks specific to your requirements. Remember to use proper error handling and ensure the correct paths are provided to avoid unintended consequences.