How to Use the Command 'git mailinfo' (with examples)

The git mailinfo command is a useful tool within the Git version control system, designed to extract patch data and authorship information from email messages. This command streamlines the process of integrating email-based patches into a repository by isolating relevant information such as the patch content and its metadata. More guidelines on the git mailinfo command can be found in the official documentation .

Use case 1: Extract the patch and author data from an email message

Code:

git mailinfo message | patch

Motivation:

A common scenario in collaborative software development is receiving patches via email from contributors. These email messages typically contain code patches and associated metadata, such as the author details. Extracting this information manually can be cumbersome and error-prone. By using git mailinfo, you can automate this task and ensure that both the data integrity and consistency are maintained.

Explanation:

• git: Invokes the Git version control system.
• mailinfo: The sub-command used to extract patch and authorship details from an email.
• message: Represents the input source, an email file containing the patch data and author information.
• | patch: The pipe (|) operator is used to pass the extracted patch data directly to the patch command, which applies the changes to the working directory.

Example output:

Author: John Doe <john.doe@example.com>
Patch extracted: my_feature_patch.diff

In this example, the command extracts the author’s name and email from the message, followed by the filename of the extracted patch. The output confirms that the patch content is successfully retrieved and ready for application.

Use case 2: Extract but remove leading and trailing whitespace

Code:

git mailinfo -k message | patch

Motivation:

Whitespace issues in patches can lead to inconsistencies when the patch is applied, potentially causing errors or unexpected behavior. Leading and trailing whitespace in the original email text may inadvertently alter the intended appearance of the code or documentation. Employing the -k option allows users to preemptively clean up these extraneous spaces, resulting in a cleaner and more reliable patch application process.

Explanation:

• -k: This option instructs git mailinfo to strip away any leading and trailing whitespace from extracted information.
• message: The email file containing the patch data.
• | patch: Sends the sanitized patch data to the patch command for application.

Example output:

Author: Jane Smith <jane.smith@example.org>
Whitespace cleaned, patch ready for application.

The output demonstrates that leading and trailing whitespace has been successfully removed, leaving behind neat and ready-to-use patch data without any unwanted spacing issues.

Use case 3: Remove everything from the body before a scissors line and retrieve the message or patch

Code:

git mailinfo --scissors message | patch

Motivation:

Some email patches may be prefixed with additional commentary or unrelated content. Conventionally, this extraneous text can be separated from the meaningful patch data by a “scissors line” (usually indicated by sequences like “–>* –”). By activating the --scissors option, you can automatically discard content above this delimiter, ensuring that only relevant patch information remains for extraction.

Explanation:

• --scissors: Activates a feature that scans for and acknowledges a scissors line, subsequently discarding all preceding content in the email.
• message: The target email file containing the scissors line and patch data.
• | patch: Directs the trimmed patch data toward the patch command for application.

Example output:

Author: Alex Brown <alex.brown@example.net>
Patch extracted, content before scissors line removed.

This output indicates the successful removal of any prefatory material over the identified scissors line, followed by an intact extraction of patch data specific to the author’s contribution.

Conclusion:

By using the git mailinfo command, developers can simplify the process of extracting patches from email messages while simultaneously improving accuracy and efficiency. Whether it’s for cleaning up whitespace, dealing with extraneous content, or extracting vital authorship details, git mailinfo supports a range of use cases, making it an indispensable tool in collaborative software development environments.