Git Hooks for Email Validation and File System Monitoring

way as they are passed to the user's Mail Transport Agent (MTA). In effect, the email given to the user's MTA, is the contents of $2 followed by the contents of $1. An example of a few common headers is shown below. Take notice of the capitalization and multi-line tab structure. From: Example <from@example.com> To: to@example.com Cc: cc@example.com, A <author@example.com>, One <one@example.com>, two@example.com Subject: PATCH-STRING Exiting with a non-zero status causes `git send-email` to abort before sending any e-mails. The following environment variables are set when executing the hook. `GIT_SENDEMAIL_FILE_COUNTER`:: A 1-based counter incremented by one for every file holding an e-mail to be sent (excluding any FIFOs). This counter does not follow the patch series counter scheme. It will always start at 1 and will end at GIT_SENDEMAIL_FILE_TOTAL. `GIT_SENDEMAIL_FILE_TOTAL`:: The total number of files that will be sent (excluding any FIFOs). This counter does not follow the patch series counter scheme. It will always be equal to the number of files being sent, whether there is a cover letter or not. These variables may for instance be used to validate patch series. The sample `sendemail-validate` hook that comes with Git checks that all sent patches (excluding the cover letter) can be applied on top of the upstream repository default branch without conflicts. Some placeholders are left for additional validation steps to be performed after all patches of a given series have been applied. fsmonitor-watchman ~~~~~~~~~~~~~~~~~~ This hook is invoked when the configuration option `core.fsmonitor` is set to `.git/hooks/fsmonitor-watchman` or `.git/hooks/fsmonitor-watchmanv2` depending on the version of the hook to use. Version 1 takes two arguments, a version (1) and the time in elapsed nanoseconds since midnight, January 1, 1970. Version 2 takes two arguments, a version (2) and a token that is used for identifying changes since the token. For watchman this would be a clock id. This version must output to stdout the new token followed by a NUL before the list of files. The hook should output to stdout the list of all files in the working directory that may have changed since the requested time. The logic should be inclusive so that it does not miss any potential changes. The paths should be relative to the root of the working directory and be separated by a single NUL. It is OK to include files which have not actually changed. All changes including newly-created and deleted files should be included. When files are renamed, both the old and the new name should be included. Git will limit what files it checks for changes as well as which directories are checked for untracked files based on the path names given. An optimized way to

This section describes two Git hooks: sendemail-validate and fsmonitor-watchman. The sendemail-validate hook is used to validate email contents and SMTP headers before sending, and can use environment variables such as GIT_SENDEMAIL_FILE_COUNTER and GIT_SENDEMAIL_FILE_TOTAL to track the number of files being sent. The fsmonitor-watchman hook is used to monitor the file system for changes and outputs a list of files that may have changed since a given time, with the goal of optimizing Git's file system checks.