The .mailmap file allows Git to handle user aliases.

It is useful to maintain a clean and consistent list of authors, for example if users changed e-mail addresses or used different names when checking in their commits.

This section provides command to identify duplicates that would require an entry in the .mailmap file.

If there is no output, then there's nothing to do !

The following command will print a list of Author names having more than one e-mail address not already aliased in mailmap.

git log --format='%aN <%aE>' | sort -u | awk -F'<' '{print $1}' | uniq -c | grep -v '^ *1 '| cut -c9-

The following command will print a list of Author e-mail addresses linked to more than one name, and not already aliased in mailmap.

git log --format='%aE %aN' | sort -u | awk '{print $1}' | uniq -c | grep -v '^ *1 ' | cut -c9-

Add aliases to the .mailmap file for each entry in the lists generated by the above commands. The following command will identify what needs to be added (replace XXX by the entry)

git log --author="XXX" --format="%aN <%aE>" | sort -u

See Reference section below for details about .mailmap file syntax.

The example below was generated on the MantisBT repository, after deleting .mailmap. For the sake of simplicity, only

1. Identify

   $ git log --format='%aN <%aE>' | sort -u | awk -F'<' '{print $1}' | uniq -c | grep -v '^ *1 '| cut -c9-
   Victor Boctor 
   
   $ git log --author="Victor Boctor" --format="%aN <%aE>" |sort -u
   Victor Boctor <vboctor@gmail.com>
   Victor Boctor <vboctor@localhost.localdomain>
   Victor Boctor <vboctor@new-host-3.home>
   Victor Boctor <victor@mantishub.com>
   Victor Boctor <victor@mantishub.net>

2. Edit .mailmap file to add aliases

   Victor Boctor <vboctor@gmail.com> root <root@localhost.localdomain>
   Victor Boctor <vboctor@gmail.com> <vboctor@localhost.localdomain>
   Victor Boctor <vboctor@gmail.com> <vboctor@new-host-3.home>
   Victor Boctor <vboctor@gmail.com> <victor@mantishub.com>
   Victor Boctor <vboctor@gmail.com> <victor@mantishub.net>

3. Check again: only a single entry is displayed now

   $ git log --author="Victor Boctor" --format="%aN <%aE>" |sort -u
   Victor Boctor <vboctor@gmail.com>

• Git manual
• Aliasing authors in Git (Atlassian blog)