Link to the issue number on GitHub within a commit message

Just include #xxx in your commit message to reference an issue without closing it.

With new GitHub issues 2.0 you can use these synonyms to reference an issue and close it (in your commit message):

fix #xxx

fixes #xxx

fixed #xxx

close #xxx

closes #xxx

closed #xxx

resolve #xxx

resolves #xxx

resolved #xxx

You can also substitute #xxx with gh-xxx.

Referencing and closing issues across repos also works:

fixes user/repo#xxx

Check out the documentation available in their Help section.

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If you want to link to a GitHub issue and close the issue, you can provide the following lines in your Git commit message:

Closes #1.
Closes GH-1.
Closes gh-1.

(Any of the three will work.) Note that this will link to the issue and also close it. You can find out more in this blog post (start watching the embedded video at about 1:40).

I'm not sure if a similar syntax will simply link to an issue without closing it.

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github adds a reference to the commit if it contains #issuenbr (discovered this by chance).

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You can also cross reference repos:

githubuser/repository#xxx

xxx being the issue number

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they have an nice write up about the new issues 2.0 on their blog https://github.blog/2011-04-09-issues-2-0-the-next-generation/

synonyms include

fixes #xxx

fixed #xxx

fix #xxx

closes #xxx

close #xxx

closed #xxx

using any of the keywords in a commit message will make your commit either mentioned or close an issue.

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In order to link the issue number to your commit message, you should add: #issue_number in your git commit message.

Example Commit Message from Udacity Git Commit Message Style Guide

feat: Summarize changes in around 50 characters or less

More detailed explanatory text, if necessary. Wrap it to about 72
characters or so. In some contexts, the first line is treated as the
subject of the commit and the rest of the text as the body. The
blank line separating the summary from the body is critical (unless
you omit the body entirely); various tools like `log`, `shortlog`
and `rebase` can get confused if you run the two together.

Explain the problem that this commit is solving. Focus on why you
are making this change as opposed to how (the code explains that).
Are there side effects or other unintuitive consequenses of this
change? Here's the place to explain them.

Further paragraphs come after blank lines.

 - Bullet points are okay, too

 - Typically a hyphen or asterisk is used for the bullet, preceded
   by a single space, with blank lines in between, but conventions
   vary here

If you use an issue tracker, put references to them at the bottom,
like this:

Resolves: #123
See also: #456, #789

You can also reference the repositories:

githubuser/repository#issue_number

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Just as addition to the other answers: If you don't even want to write the commit message with the issue number and happen to use Eclipse for development, then you can install the eGit and Mylyn plugins as well as the GitHub connector for Mylyn. Eclipse can then automatically track which issue you are working on and automatically fill the commit message, including the issue number as shown in all the other answers.

For more details about that setup see http://wiki.eclipse.org/EGit/GitHub/UserGuide

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One of my first projects as a programmer was a gem called stagecoach that (among other things) allowed the automatic adding of a github issue number to every commit message on a branch, which is a part of the question that hasn't really been answered.

Essentially when creating a branch you'd use a custom command (something like stagecoach -b <branch_name> -g <issue_number>), and the issue number would then be assigned to that branch in a yml file. There was then a commit hook that appended the issue number to the commit message automatically.

I wouldn't recommend it for production use as at the time I'd only been programming for a few months and I no longer maintain it, but it may be of interest to somebody.

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