How to Use the Command 'mmv' (with Examples)

The mmv command is a powerful utility used to move, rename, or copy files in bulk. It allows users to perform complex file operations quickly and efficiently using a pattern-based approach. This can save a significant amount of time and effort when working with numerous files that need to be managed in a consistent way. The command is particularly useful in scripting and batch operations, making it a valuable tool for system administrators and developers.

Use Case 1: Rename All Files with a Certain Extension to a Different Extension

Code:

mmv "*.old_extension" "#1.new_extension"

Motivation:
Renaming file extensions from one type to another is a common task, especially when dealing with software projects or data conversions that require a specific file type. Imagine you have a directory filled with configuration files ending in .conf and you want to change them all to .cfg to comply with a new system requirement. Manually renaming each file would be tedious and prone to error, but with mmv, this task becomes quick and painless.

Explanation:

• *.old_extension: This wildcard pattern matches all files with the specified old extension. The asterisk * acts as a placeholder for any number of characters before the extension.
• #1.new_extension: The #1 is a placeholder that references the portion of the filename matched by *. The command replaces the old extension with the new one while keeping the filename intact.

Example Output:
Before using the command, you have files like document1.old_extension, document2.old_extension, etc. After executing the command, they become document1.new_extension, document2.new_extension, etc.

Use Case 2: Copy report6part4.txt to ./french/rapport6partie4.txt Along With All Similarly Named Files

Code:

mmv -c "report*part*.txt" "./french/rapport#1partie#2.txt"

Motivation:
When working with files that follow a particular naming convention, it’s often necessary to not only rename but also re-organize them into different directories for better structure or localization. Suppose you have a series of reports segmented by parts and chapters, and you need to localize their filenames into French while also organizing them into a specific directory. This command helps automate the repetitive process, alleviating human error and saving time.

Explanation:

• -c: This option copies files instead of moving them.
• "report*part*.txt": This pattern selects files that match the naming convention of a report (e.g., report6part4.txt).
• "./french/rapport#1partie#2.txt": The target pattern where #1 represents the first wildcard match (* after report), and #2 the second (* after part). This maps the original filename structure into the new localized format.

Example Output:
From files such as report6part4.txt, report9part1.txt, etc., in your working directory, they will be copied as ./french/rapport6partie4.txt, ./french/rapport9partie1.txt, etc.

Use Case 3: Append All .txt Files Into One File

Code:

mmv -a "*.txt" "all.txt"

Motivation:
Combining multiple text files into a single file is a common requirement, especially when gathering data logs or documentations that are split across multiple files. This operation is beneficial for creating a consolidated view or backup of text data without manually opening and copying each file’s content. mmv simplifies this aggregation by appending the content seamlessly.

Explanation:

• -a: This flag appends the contents of each source file to the target file.
• "*.txt": A wildcard pattern matching all text files in the current directory.
• "all.txt": The destination file where all contents will be appended. It will either create a new file if it does not exist or add to the end of an existing file.

Example Output:
All individual text files such as file1.txt, file2.txt, etc., are merged into a single file all.txt, with their contents sequentially appended inside.

Use Case 4: Convert Dates in Filenames from “M-D-Y” Format to “D-M-Y” Format

Code:

mmv "[0-1][0-9]-[0-3][0-9]-[0-9][0-9][0-9][0-9].txt" "#3#4-#1#2-#5#6#7#8.txt"

Motivation:
Renaming files to reflect a different date format might be necessary for consistency with international standards or compliance with organizational naming conventions. Changing a U.S. date format (Month-Day-Year) to a European format (Day-Month-Year) can help prevent misunderstandings among a global team. This command provides an efficient way to make this conversion accurately across all relevant files.

Explanation:

• "[0-1][0-9]-[0-3][0-9]-[0-9][0-9][0-9][0-9].txt": The pattern recognizes date format where month and day are comprised of two digits each, separated by -, followed by a four-digit year, e.g., 11-05-2023.txt.
• "#3#4-#1#2-#5#6#7#8.txt": Here, #3#4 swaps to position where the day is in the original filename and #1#2 where the month resided. This rearranges the order to DD-MM-YYYY.

Example Output:
A file named 11-05-2023.txt would be renamed to 05-11-2023.txt, altering the format from Month-Day-Year to Day-Month-Year.

Conclusion:

The mmv command provides substantial utility for batch file renaming, moving, copying, and content appending, transforming complex file management tasks into simple command-line operations. Its pattern-based approach significantly reduces manual effort and errors in handling large numbers of files, making it an essential tool for anyone working extensively with file systems.