Bash by Example: Batch Rename Files

Bash 5.0+

Mass renaming files using string manipulation and loops for bulk file operations, implementing pattern-based renaming with parameter expansion, changing file extensions across multiple files, adding prefixes or suffixes systematically, and performing complex filename transformations without external tools.

Code

#!/bin/bash

# Setup dummy files
mkdir -p photos
touch photos/img_001.jpg photos/img_002.jpg photos/img_003.png

echo "Original files:"
ls photos

echo -e "\nRenaming .jpg to .jpeg..."

for file in photos/*.jpg; do
    # Check if file exists (in case glob matches nothing)
    [ -e "$file" ] || continue

    # String Manipulation
    # ${var%pattern} removes shortest match from END
    base_name="${file%.jpg}"
    
    # Construct new name
    new_name="${base_name}.jpeg"
    
    mv "$file" "$new_name"
    echo "Renamed: $file -> $new_name"
done

echo -e "\nAdding prefix 'vacation_'..."
for file in photos/*; do
    # Get just the filename without path
    filename=$(basename "$file")
    dir=$(dirname "$file")
    
    mv "$file" "$dir/vacation_$filename"
done

echo -e "\nFinal files:"
ls photos
rm -rf photos

Explanation

Renaming a single file is easy with mv, but renaming hundreds of files—changing extensions, adding dates, or fixing capitalization—requires automation. While there is a dedicated rename utility (Perl-based) on many systems, it is not standard everywhere. Bash's built-in string manipulation capabilities allow you to write portable batch rename scripts without external dependencies.

The key feature here is Parameter Expansion. The syntax ${variable%pattern} removes the shortest match of pattern from the end of the variable. For example, if file="image.jpg", then ${file%.jpg} evaluates to "image". This allows you to strip the old extension and append a new one.

Another common requirement is adding a prefix. This involves separating the directory path from the filename using dirname and basename (or more parameter expansion), modifying the filename string, and then reassembling the path for the mv command.

Code Breakdown

18

${file%.jpg} is a standard Bash string operation. It strips the suffix ".jpg". If the variable doesn't end with that pattern, it remains unchanged.

30

basename and dirname are essential when looping over globs like dir/*. The variable $file contains the full path photos/img.jpg. We need to split it to rename just the file part, not the directory part.

Samplebadu

Bash by Example: Batch Rename Files

Code

Explanation

Code Breakdown