contrib/hooks/post-receive-email - jrn/git - Git at Google

 #!/bin/sh
 #
 # Copyright (c) 2007 Andy Parkins
 #
 # An example hook script to mail out commit update information.  This hook
 # sends emails listing new revisions to the repository introduced by the
 # change being reported.  The rule is that (for branch updates) each commit
 # will appear on one email and one email only.
 #
 # This hook is stored in the contrib/hooks directory.  Your distribution
 # will have put this somewhere standard.  You should make this script
 # executable then link to it in the repository you would like to use it in.
 # For example, on debian the hook is stored in
 # /usr/share/git-core/contrib/hooks/post-receive-email:
 #
 #  chmod a+x post-receive-email
 #  cd /path/to/your/repository.git
 #  ln -sf /usr/share/git-core/contrib/hooks/post-receive-email hooks/post-receive
 #
 # This hook script assumes it is enabled on the central repository of a
 # project, with all users pushing only to it and not between each other.  It
 # will still work if you don't operate in that style, but it would become
 # possible for the email to be from someone other than the person doing the
 # push.
 #
 # To help with debugging and use on pre-v1.5.1 git servers, this script will
 # also obey the interface of hooks/update, taking its arguments on the
 # command line.  Unfortunately, hooks/update is called once for each ref.
 # To avoid firing one email per ref, this script just prints its output to
 # the screen when used in this mode.  The output can then be redirected if
 # wanted.
 #
 # Config
 # ------
 # hooks.mailinglist
 #   This is the list that all pushes will go to; leave it blank to not send
 #   emails for every ref update.
 # hooks.announcelist
 #   This is the list that all pushes of annotated tags will go to.  Leave it
 #   blank to default to the mailinglist field.  The announce emails lists
 #   the short log summary of the changes since the last annotated tag.
 # hooks.envelopesender
 #   If set then the -f option is passed to sendmail to allow the envelope
 #   sender address to be set
 # hooks.emailprefix
 #   All emails have their subjects prefixed with this prefix, or "[SCM]"
 #   if emailprefix is unset, to aid filtering
 # hooks.showrev
 #   The shell command used to format each revision in the email, with
 #   "%s" replaced with the commit id.  Defaults to "git rev-list -1
 #   --pretty %s", displaying the commit id, author, date and log
 #   message.  To list full patches separated by a blank line, you
 #   could set this to "git show -C %s; echo".
 #   To list a gitweb/cgit URL *and* a full patch for each change set, use this:
 #     "t=%s; printf 'http://.../?id=%%s' \$t; echo;echo; git show -C \$t; echo"
 #   Be careful if "..." contains things that will be expanded by shell "eval"
 #   or printf.
 # hooks.emailmaxlines
 #   The maximum number of lines that should be included in the generated
 #   email body. If not specified, there is no limit.
 #   Lines beyond the limit are suppressed and counted, and a final
 #   line is added indicating the number of suppressed lines.
 # hooks.diffopts
 #   Alternate options for the git diff-tree invocation that shows changes.
 #   Default is "--stat --summary --find-copies-harder". Add -p to those
 #   options to include a unified diff of changes in addition to the usual
 #   summary output.
 #
 # Notes
 # -----
 # All emails include the headers "X-Git-Refname", "X-Git-Oldrev",
 # "X-Git-Newrev", and "X-Git-Reftype" to enable fine tuned filtering and
 # give information for debugging.
 #

 # ---------------------------- Functions

 #
 # Function to prepare for email generation. This decides what type
 # of update this is and whether an email should even be generated.
 #
 prep_for_email()
 {
 	# --- Arguments
 	oldrev=$(git rev-parse $1)
 	newrev=$(git rev-parse $2)
 	refname="$3"

 	# --- Interpret
 	# 0000->1234 (create)
 	# 1234->2345 (update)
 	# 2345->0000 (delete)
 	if expr "$oldrev" : '0*$' >/dev/null
 	then
 		change_type="create"
 	else
 		if expr "$newrev" : '0*$' >/dev/null
 		then
 			change_type="delete"
 		else
 			change_type="update"
 		fi
 	fi

 	# --- Get the revision types
 	newrev_type=$(git cat-file -t $newrev 2> /dev/null)
 	oldrev_type=$(git cat-file -t "$oldrev" 2> /dev/null)
 	case "$change_type" in
 	create|update)
 		rev="$newrev"
 		rev_type="$newrev_type"
 		;;
 	delete)
 		rev="$oldrev"
 		rev_type="$oldrev_type"
 		;;
 	esac

 	# The revision type tells us what type the commit is, combined with
 	# the location of the ref we can decide between
 	#  - working branch
 	#  - tracking branch
 	#  - unannoted tag
 	#  - annotated tag
 	case "$refname","$rev_type" in
 		refs/tags/*,commit)
 			# un-annotated tag
 			refname_type="tag"
 			short_refname=${refname##refs/tags/}
 			;;
 		refs/tags/*,tag)
 			# annotated tag
 			refname_type="annotated tag"
 			short_refname=${refname##refs/tags/}
 			# change recipients
 			if [ -n "$announcerecipients" ]; then
 				recipients="$announcerecipients"
 			fi
 			;;
 		refs/heads/*,commit)
 			# branch
 			refname_type="branch"
 			short_refname=${refname##refs/heads/}
 			;;
 		refs/remotes/*,commit)
 			# tracking branch
 			refname_type="tracking branch"
 			short_refname=${refname##refs/remotes/}
 			echo >&2 "*** Push-update of tracking branch, $refname"
 			echo >&2 "***  - no email generated."
 			return 1
 			;;
 		*)
 			# Anything else (is there anything else?)
 			echo >&2 "*** Unknown type of update to $refname ($rev_type)"
 			echo >&2 "***  - no email generated"
 			return 1
 			;;
 	esac

 	# Check if we've got anyone to send to
 	if [ -z "$recipients" ]; then
 		case "$refname_type" in
 			"annotated tag")
 				config_name="hooks.announcelist"
 				;;
 			*)
 				config_name="hooks.mailinglist"
 				;;
 		esac
 		echo >&2 "*** $config_name is not set so no email will be sent"
 		echo >&2 "*** for $refname update $oldrev->$newrev"
 		return 1
 	fi

 	return 0
 }

 #
 # Top level email generation function.  This calls the appropriate
 # body-generation routine after outputting the common header.
 #
 # Note this function doesn't actually generate any email output, that is
 # taken care of by the functions it calls:
 #  - generate_email_header
 #  - generate_create_XXXX_email
 #  - generate_update_XXXX_email
 #  - generate_delete_XXXX_email
 #  - generate_email_footer
 #
 # Note also that this function cannot 'exit' from the script; when this
 # function is running (in hook script mode), the send_mail() function
 # is already executing in another process, connected via a pipe, and
 # if this function exits without, whatever has been generated to that
 # point will be sent as an email... even if nothing has been generated.
 #
 generate_email()
 {
 	# Email parameters
 	# The email subject will contain the best description of the ref
 	# that we can build from the parameters
 	describe=$(git describe $rev 2>/dev/null)
 	if [ -z "$describe" ]; then
 		describe=$rev
 	fi

 	generate_email_header

 	# Call the correct body generation function
 	fn_name=general
 	case "$refname_type" in
 	"tracking branch"|branch)
 		fn_name=branch
 		;;
 	"annotated tag")
 		fn_name=atag
 		;;
 	esac

 	if [ -z "$maxlines" ]; then
 		generate_${change_type}_${fn_name}_email
 	else
 		generate_${change_type}_${fn_name}_email | limit_lines $maxlines
 	fi

 	generate_email_footer
 }

 generate_email_header()
 {
 	# --- Email (all stdout will be the email)
 	# Generate header
 	cat <<-EOF
 	To: $recipients
 	Subject: ${emailprefix}$projectdesc $refname_type $short_refname ${change_type}d. $describe
 	X-Git-Refname: $refname
 	X-Git-Reftype: $refname_type
 	X-Git-Oldrev: $oldrev
 	X-Git-Newrev: $newrev

 	This is an automated email from the git hooks/post-receive script. It was
 	generated because a ref change was pushed to the repository containing
 	the project "$projectdesc".

 	The $refname_type, $short_refname has been ${change_type}d
 	EOF
 }

 generate_email_footer()
 {
 	SPACE=" "
 	cat <<-EOF


 	hooks/post-receive
 	--${SPACE}
 	$projectdesc
 	EOF
 }

 # --------------- Branches

 #
 # Called for the creation of a branch
 #
 generate_create_branch_email()
 {
 	# This is a new branch and so oldrev is not valid
 	echo "        at  $newrev ($newrev_type)"
 	echo ""

 	echo $LOGBEGIN
 	show_new_revisions
 	echo $LOGEND
 }

 #
 # Called for the change of a pre-existing branch
 #
 generate_update_branch_email()
 {
 	# Consider this:
 	#   1 --- 2 --- O --- X --- 3 --- 4 --- N
 	#
 	# O is $oldrev for $refname
 	# N is $newrev for $refname
 	# X is a revision pointed to by some other ref, for which we may
 	#   assume that an email has already been generated.
 	# In this case we want to issue an email containing only revisions
 	# 3, 4, and N.  Given (almost) by
 	#
 	#  git rev-list N ^O --not --all
 	#
 	# The reason for the "almost", is that the "--not --all" will take
 	# precedence over the "N", and effectively will translate to
 	#
 	#  git rev-list N ^O ^X ^N
 	#
 	# So, we need to build up the list more carefully.  git rev-parse
 	# will generate a list of revs that may be fed into git rev-list.
 	# We can get it to make the "--not --all" part and then filter out
 	# the "^N" with:
 	#
 	#  git rev-parse --not --all | grep -v N
 	#
 	# Then, using the --stdin switch to git rev-list we have effectively
 	# manufactured
 	#
 	#  git rev-list N ^O ^X
 	#
 	# This leaves a problem when someone else updates the repository
 	# while this script is running.  Their new value of the ref we're
 	# working on would be included in the "--not --all" output; and as
 	# our $newrev would be an ancestor of that commit, it would exclude
 	# all of our commits.  What we really want is to exclude the current
 	# value of $refname from the --not list, rather than N itself.  So:
 	#
 	#  git rev-parse --not --all | grep -v $(git rev-parse $refname)
 	#
 	# Get's us to something pretty safe (apart from the small time
 	# between refname being read, and git rev-parse running - for that,
 	# I give up)
 	#
 	#
 	# Next problem, consider this:
 	#   * --- B --- * --- O ($oldrev)
 	#          \
 	#           * --- X --- * --- N ($newrev)
 	#
 	# That is to say, there is no guarantee that oldrev is a strict
 	# subset of newrev (it would have required a --force, but that's
 	# allowed).  So, we can't simply say rev-list $oldrev..$newrev.
 	# Instead we find the common base of the two revs and list from
 	# there.
 	#
 	# As above, we need to take into account the presence of X; if
 	# another branch is already in the repository and points at some of
 	# the revisions that we are about to output - we don't want them.
 	# The solution is as before: git rev-parse output filtered.
 	#
 	# Finally, tags: 1 --- 2 --- O --- T --- 3 --- 4 --- N
 	#
 	# Tags pushed into the repository generate nice shortlog emails that
 	# summarise the commits between them and the previous tag.  However,
 	# those emails don't include the full commit messages that we output
 	# for a branch update.  Therefore we still want to output revisions
 	# that have been output on a tag email.
 	#
 	# Luckily, git rev-parse includes just the tool.  Instead of using
 	# "--all" we use "--branches"; this has the added benefit that
 	# "remotes/" will be ignored as well.

 	# List all of the revisions that were removed by this update, in a
 	# fast-forward update, this list will be empty, because rev-list O
 	# ^N is empty.  For a non-fast-forward, O ^N is the list of removed
 	# revisions
 	fast_forward=""
 	rev=""
 	for rev in $(git rev-list $newrev..$oldrev)
 	do
 		revtype=$(git cat-file -t "$rev")
 		echo "  discards  $rev ($revtype)"
 	done
 	if [ -z "$rev" ]; then
 		fast_forward=1
 	fi

 	# List all the revisions from baserev to newrev in a kind of
 	# "table-of-contents"; note this list can include revisions that
 	# have already had notification emails and is present to show the
 	# full detail of the change from rolling back the old revision to
 	# the base revision and then forward to the new revision
 	for rev in $(git rev-list $oldrev..$newrev)
 	do
 		revtype=$(git cat-file -t "$rev")
 		echo "       via  $rev ($revtype)"
 	done

 	if [ "$fast_forward" ]; then
 		echo "      from  $oldrev ($oldrev_type)"
 	else
 		#  1. Existing revisions were removed.  In this case newrev
 		#     is a subset of oldrev - this is the reverse of a
 		#     fast-forward, a rewind
 		#  2. New revisions were added on top of an old revision,
 		#     this is a rewind and addition.

 		# (1) certainly happened, (2) possibly.  When (2) hasn't
 		# happened, we set a flag to indicate that no log printout
 		# is required.

 		echo ""

 		# Find the common ancestor of the old and new revisions and
 		# compare it with newrev
 		baserev=$(git merge-base $oldrev $newrev)
 		rewind_only=""
 		if [ "$baserev" = "$newrev" ]; then
 			echo "This update discarded existing revisions and left the branch pointing at"
 			echo "a previous point in the repository history."
 			echo ""
 			echo " * -- * -- N ($newrev)"
 			echo "            \\"
 			echo "             O -- O -- O ($oldrev)"
 			echo ""
 			echo "The removed revisions are not necessarily gone - if another reference"
 			echo "still refers to them they will stay in the repository."
 			rewind_only=1
 		else
 			echo "This update added new revisions after undoing existing revisions.  That is"
 			echo "to say, the old revision is not a strict subset of the new revision.  This"
 			echo "situation occurs when you --force push a change and generate a repository"
 			echo "containing something like this:"
 			echo ""
 			echo " * -- * -- B -- O -- O -- O ($oldrev)"
 			echo "            \\"
 			echo "             N -- N -- N ($newrev)"
 			echo ""
 			echo "When this happens we assume that you've already had alert emails for all"
 			echo "of the O revisions, and so we here report only the revisions in the N"
 			echo "branch from the common base, B."
 		fi
 	fi

 	echo ""
 	if [ -z "$rewind_only" ]; then
 		echo "Those revisions listed above that are new to this repository have"
 		echo "not appeared on any other notification email; so we list those"
 		echo "revisions in full, below."

 		echo ""
 		echo $LOGBEGIN
 		show_new_revisions

 		# XXX: Need a way of detecting whether git rev-list actually
 		# outputted anything, so that we can issue a "no new
 		# revisions added by this update" message

 		echo $LOGEND
 	else
 		echo "No new revisions were added by this update."
 	fi

 	# The diffstat is shown from the old revision to the new revision.
 	# This is to show the truth of what happened in this change.
 	# There's no point showing the stat from the base to the new
 	# revision because the base is effectively a random revision at this
 	# point - the user will be interested in what this revision changed
 	# - including the undoing of previous revisions in the case of
 	# non-fast-forward updates.
 	echo ""
 	echo "Summary of changes:"
 	git diff-tree $diffopts $oldrev..$newrev
 }

 #
 # Called for the deletion of a branch
 #
 generate_delete_branch_email()
 {
 	echo "       was  $oldrev"
 	echo ""
 	echo $LOGBEGIN
 	git show -s --pretty=oneline $oldrev
 	echo $LOGEND
 }

 # --------------- Annotated tags

 #
 # Called for the creation of an annotated tag
 #
 generate_create_atag_email()
 {
 	echo "        at  $newrev ($newrev_type)"

 	generate_atag_email
 }

 #
 # Called for the update of an annotated tag (this is probably a rare event
 # and may not even be allowed)
 #
 generate_update_atag_email()
 {
 	echo "        to  $newrev ($newrev_type)"
 	echo "      from  $oldrev (which is now obsolete)"

 	generate_atag_email
 }

 #
 # Called when an annotated tag is created or changed
 #
 generate_atag_email()
 {
 	# Use git for-each-ref to pull out the individual fields from the
 	# tag
 	eval $(git for-each-ref --shell --format='
 	tagobject=%(*objectname)
 	tagtype=%(*objecttype)
 	tagger=%(taggername)
 	tagged=%(taggerdate)' $refname
 	)

 	echo "   tagging  $tagobject ($tagtype)"
 	case "$tagtype" in
 	commit)

 		# If the tagged object is a commit, then we assume this is a
 		# release, and so we calculate which tag this tag is
 		# replacing
 		prevtag=$(git describe --abbrev=0 $newrev^ 2>/dev/null)

 		if [ -n "$prevtag" ]; then
 			echo "  replaces  $prevtag"
 		fi
 		;;
 	*)
 		echo "    length  $(git cat-file -s $tagobject) bytes"
 		;;
 	esac
 	echo " tagged by  $tagger"
 	echo "        on  $tagged"

 	echo ""
 	echo $LOGBEGIN

 	# Show the content of the tag message; this might contain a change
 	# log or release notes so is worth displaying.
 	git cat-file tag $newrev | sed -e '1,/^$/d'

 	echo ""
 	case "$tagtype" in
 	commit)
 		# Only commit tags make sense to have rev-list operations
 		# performed on them
 		if [ -n "$prevtag" ]; then
 			# Show changes since the previous release
 			git rev-list --pretty=short "$prevtag..$newrev" | git shortlog
 		else
 			# No previous tag, show all the changes since time
 			# began
 			git rev-list --pretty=short $newrev | git shortlog
 		fi
 		;;
 	*)
 		# XXX: Is there anything useful we can do for non-commit
 		# objects?
 		;;
 	esac

 	echo $LOGEND
 }

 #
 # Called for the deletion of an annotated tag
 #
 generate_delete_atag_email()
 {
 	echo "       was  $oldrev"
 	echo ""
 	echo $LOGBEGIN
 	git show -s --pretty=oneline $oldrev
 	echo $LOGEND
 }

 # --------------- General references

 #
 # Called when any other type of reference is created (most likely a
 # non-annotated tag)
 #
 generate_create_general_email()
 {
 	echo "        at  $newrev ($newrev_type)"

 	generate_general_email
 }

 #
 # Called when any other type of reference is updated (most likely a
 # non-annotated tag)
 #
 generate_update_general_email()
 {
 	echo "        to  $newrev ($newrev_type)"
 	echo "      from  $oldrev"

 	generate_general_email
 }

 #
 # Called for creation or update of any other type of reference
 #
 generate_general_email()
 {
 	# Unannotated tags are more about marking a point than releasing a
 	# version; therefore we don't do the shortlog summary that we do for
 	# annotated tags above - we simply show that the point has been
 	# marked, and print the log message for the marked point for
 	# reference purposes
 	#
 	# Note this section also catches any other reference type (although
 	# there aren't any) and deals with them in the same way.

 	echo ""
 	if [ "$newrev_type" = "commit" ]; then
 		echo $LOGBEGIN
 		git show --no-color --root -s --pretty=medium $newrev
 		echo $LOGEND
 	else
 		# What can we do here?  The tag marks an object that is not
 		# a commit, so there is no log for us to display.  It's
 		# probably not wise to output git cat-file as it could be a
 		# binary blob.  We'll just say how big it is
 		echo "$newrev is a $newrev_type, and is $(git cat-file -s $newrev) bytes long."
 	fi
 }

 #
 # Called for the deletion of any other type of reference
 #
 generate_delete_general_email()
 {
 	echo "       was  $oldrev"
 	echo ""
 	echo $LOGBEGIN
 	git show -s --pretty=oneline $oldrev
 	echo $LOGEND
 }


 # --------------- Miscellaneous utilities

 #
 # Show new revisions as the user would like to see them in the email.
 #
 show_new_revisions()
 {
 	# This shows all log entries that are not already covered by
 	# another ref - i.e. commits that are now accessible from this
 	# ref that were previously not accessible
 	# (see generate_update_branch_email for the explanation of this
 	# command)

 	# Revision range passed to rev-list differs for new vs. updated
 	# branches.
 	if [ "$change_type" = create ]
 	then
 		# Show all revisions exclusive to this (new) branch.
 		revspec=$newrev
 	else
 		# Branch update; show revisions not part of $oldrev.
 		revspec=$oldrev..$newrev
 	fi

 	other_branches=$(git for-each-ref --format='%(refname)' refs/heads/ |
 	    grep -F -v $refname)
 	git rev-parse --not $other_branches |
 	if [ -z "$custom_showrev" ]
 	then
 		git rev-list --pretty --stdin $revspec
 	else
 		git rev-list --stdin $revspec |
 		while read onerev
 		do
 			eval $(printf "$custom_showrev" $onerev)
 		done
 	fi
 }


 limit_lines()
 {
 	lines=0
 	skipped=0
 	while IFS="" read -r line; do
 		lines=$((lines + 1))
 		if [ $lines -gt $1 ]; then
 			skipped=$((skipped + 1))
 		else
 			printf "%s\n" "$line"
 		fi
 	done
 	if [ $skipped -ne 0 ]; then
 		echo "... $skipped lines suppressed ..."
 	fi
 }


 send_mail()
 {
 	if [ -n "$envelopesender" ]; then
 		/usr/sbin/sendmail -t -f "$envelopesender"
 	else
 		/usr/sbin/sendmail -t
 	fi
 }

 # ---------------------------- main()

 # --- Constants
 LOGBEGIN="- Log -----------------------------------------------------------------"
 LOGEND="-----------------------------------------------------------------------"

 # --- Config
 # Set GIT_DIR either from the working directory, or from the environment
 # variable.
 GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
 if [ -z "$GIT_DIR" ]; then
 	echo >&2 "fatal: post-receive: GIT_DIR not set"
 	exit 1
 fi

 projectdesc=$(sed -ne '1p' "$GIT_DIR/description" 2>/dev/null)
 # Check if the description is unchanged from it's default, and shorten it to
 # a more manageable length if it is
 if expr "$projectdesc" : "Unnamed repository.*$" >/dev/null
 then
 	projectdesc="UNNAMED PROJECT"
 fi

 recipients=$(git config hooks.mailinglist)
 announcerecipients=$(git config hooks.announcelist)
 envelopesender=$(git config hooks.envelopesender)
 emailprefix=$(git config hooks.emailprefix || echo '[SCM] ')
 custom_showrev=$(git config hooks.showrev)
 maxlines=$(git config hooks.emailmaxlines)
 diffopts=$(git config hooks.diffopts)
 : ${diffopts:="--stat --summary --find-copies-harder"}

 # --- Main loop
 # Allow dual mode: run from the command line just like the update hook, or
 # if no arguments are given then run as a hook script
 if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
 	# Output to the terminal in command line mode - if someone wanted to
 	# resend an email; they could redirect the output to sendmail
 	# themselves
 	prep_for_email $2 $3 $1 && PAGER= generate_email
 else
 	while read oldrev newrev refname
 	do
 		prep_for_email $oldrev $newrev $refname || continue
 		generate_email $maxlines | send_mail
 	done
 fi
	#!/bin/sh
	#
	# Copyright (c) 2007 Andy Parkins
	#
	# An example hook script to mail out commit update information. This hook
	# sends emails listing new revisions to the repository introduced by the
	# change being reported. The rule is that (for branch updates) each commit
	# will appear on one email and one email only.
	#
	# This hook is stored in the contrib/hooks directory. Your distribution
	# will have put this somewhere standard. You should make this script
	# executable then link to it in the repository you would like to use it in.
	# For example, on debian the hook is stored in
	# /usr/share/git-core/contrib/hooks/post-receive-email:
	#
	# chmod a+x post-receive-email
	# cd /path/to/your/repository.git
	# ln -sf /usr/share/git-core/contrib/hooks/post-receive-email hooks/post-receive
	#
	# This hook script assumes it is enabled on the central repository of a
	# project, with all users pushing only to it and not between each other. It
	# will still work if you don't operate in that style, but it would become
	# possible for the email to be from someone other than the person doing the
	# push.
	#
	# To help with debugging and use on pre-v1.5.1 git servers, this script will
	# also obey the interface of hooks/update, taking its arguments on the
	# command line. Unfortunately, hooks/update is called once for each ref.
	# To avoid firing one email per ref, this script just prints its output to
	# the screen when used in this mode. The output can then be redirected if
	# wanted.
	#
	# Config
	# ------
	# hooks.mailinglist
	# This is the list that all pushes will go to; leave it blank to not send
	# emails for every ref update.
	# hooks.announcelist
	# This is the list that all pushes of annotated tags will go to. Leave it
	# blank to default to the mailinglist field. The announce emails lists
	# the short log summary of the changes since the last annotated tag.
	# hooks.envelopesender
	# If set then the -f option is passed to sendmail to allow the envelope
	# sender address to be set
	# hooks.emailprefix
	# All emails have their subjects prefixed with this prefix, or "[SCM]"
	# if emailprefix is unset, to aid filtering
	# hooks.showrev
	# The shell command used to format each revision in the email, with
	# "%s" replaced with the commit id. Defaults to "git rev-list -1
	# --pretty %s", displaying the commit id, author, date and log
	# message. To list full patches separated by a blank line, you
	# could set this to "git show -C %s; echo".
	# To list a gitweb/cgit URL and a full patch for each change set, use this:
	# "t=%s; printf 'http://.../?id=%%s' \$t; echo;echo; git show -C \$t; echo"
	# Be careful if "..." contains things that will be expanded by shell "eval"
	# or printf.
	# hooks.emailmaxlines
	# The maximum number of lines that should be included in the generated
	# email body. If not specified, there is no limit.
	# Lines beyond the limit are suppressed and counted, and a final
	# line is added indicating the number of suppressed lines.
	# hooks.diffopts
	# Alternate options for the git diff-tree invocation that shows changes.
	# Default is "--stat --summary --find-copies-harder". Add -p to those
	# options to include a unified diff of changes in addition to the usual
	# summary output.
	#
	# Notes
	# -----
	# All emails include the headers "X-Git-Refname", "X-Git-Oldrev",
	# "X-Git-Newrev", and "X-Git-Reftype" to enable fine tuned filtering and
	# give information for debugging.
	#

	# ---------------------------- Functions

	#
	# Function to prepare for email generation. This decides what type
	# of update this is and whether an email should even be generated.
	#
	prep_for_email()
	{
	# --- Arguments
	oldrev=$(git rev-parse $1)
	newrev=$(git rev-parse $2)
	refname="$3"

	# --- Interpret
	# 0000->1234 (create)
	# 1234->2345 (update)
	# 2345->0000 (delete)
	if expr "$oldrev" : '0*$' >/dev/null
	then
	change_type="create"
	else
	if expr "$newrev" : '0*$' >/dev/null
	then
	change_type="delete"
	else
	change_type="update"
	fi
	fi

	# --- Get the revision types
	newrev_type=$(git cat-file -t $newrev 2> /dev/null)
	oldrev_type=$(git cat-file -t "$oldrev" 2> /dev/null)
	case "$change_type" in
	create\|update)
	rev="$newrev"
	rev_type="$newrev_type"
	;;
	delete)
	rev="$oldrev"
	rev_type="$oldrev_type"
	;;
	esac

	# The revision type tells us what type the commit is, combined with
	# the location of the ref we can decide between
	# - working branch
	# - tracking branch
	# - unannoted tag
	# - annotated tag
	case "$refname","$rev_type" in
	refs/tags/*,commit)
	# un-annotated tag
	refname_type="tag"
	short_refname=${refname##refs/tags/}
	;;
	refs/tags/*,tag)
	# annotated tag
	refname_type="annotated tag"
	short_refname=${refname##refs/tags/}
	# change recipients
	if [ -n "$announcerecipients" ]; then
	recipients="$announcerecipients"
	fi
	;;
	refs/heads/*,commit)
	# branch
	refname_type="branch"
	short_refname=${refname##refs/heads/}
	;;
	refs/remotes/*,commit)
	# tracking branch
	refname_type="tracking branch"
	short_refname=${refname##refs/remotes/}
	echo >&2 "*** Push-update of tracking branch, $refname"
	echo >&2 "*** - no email generated."
	return 1
	;;
	*)
	# Anything else (is there anything else?)
	echo >&2 "*** Unknown type of update to $refname ($rev_type)"
	echo >&2 "*** - no email generated"
	return 1
	;;
	esac

	# Check if we've got anyone to send to
	if [ -z "$recipients" ]; then
	case "$refname_type" in
	"annotated tag")
	config_name="hooks.announcelist"
	;;
	*)
	config_name="hooks.mailinglist"
	;;
	esac
	echo >&2 "*** $config_name is not set so no email will be sent"
	echo >&2 "*** for $refname update $oldrev->$newrev"
	return 1
	fi

	return 0
	}

	#
	# Top level email generation function. This calls the appropriate
	# body-generation routine after outputting the common header.
	#
	# Note this function doesn't actually generate any email output, that is
	# taken care of by the functions it calls:
	# - generate_email_header
	# - generate_create_XXXX_email
	# - generate_update_XXXX_email
	# - generate_delete_XXXX_email
	# - generate_email_footer
	#
	# Note also that this function cannot 'exit' from the script; when this
	# function is running (in hook script mode), the send_mail() function
	# is already executing in another process, connected via a pipe, and
	# if this function exits without, whatever has been generated to that
	# point will be sent as an email... even if nothing has been generated.
	#
	generate_email()
	{
	# Email parameters
	# The email subject will contain the best description of the ref
	# that we can build from the parameters
	describe=$(git describe $rev 2>/dev/null)
	if [ -z "$describe" ]; then
	describe=$rev
	fi

	generate_email_header

	# Call the correct body generation function
	fn_name=general
	case "$refname_type" in
	"tracking branch"\|branch)
	fn_name=branch
	;;
	"annotated tag")
	fn_name=atag
	;;
	esac

	if [ -z "$maxlines" ]; then
	generate_${change_type}_${fn_name}_email
	else
	generate_${change_type}_${fn_name}_email \| limit_lines $maxlines
	fi

	generate_email_footer
	}

	generate_email_header()
	{
	# --- Email (all stdout will be the email)
	# Generate header
	cat <<-EOF
	To: $recipients
	Subject: ${emailprefix}$projectdesc $refname_type $short_refname ${change_type}d. $describe
	X-Git-Refname: $refname
	X-Git-Reftype: $refname_type
	X-Git-Oldrev: $oldrev
	X-Git-Newrev: $newrev

	This is an automated email from the git hooks/post-receive script. It was
	generated because a ref change was pushed to the repository containing
	the project "$projectdesc".

	The $refname_type, $short_refname has been ${change_type}d
	EOF
	}

	generate_email_footer()
	{
	SPACE=" "
	cat <<-EOF


	hooks/post-receive
	--${SPACE}
	$projectdesc
	EOF
	}

	# --------------- Branches

	#
	# Called for the creation of a branch
	#
	generate_create_branch_email()
	{
	# This is a new branch and so oldrev is not valid
	echo " at $newrev ($newrev_type)"
	echo ""

	echo $LOGBEGIN
	show_new_revisions
	echo $LOGEND
	}

	#
	# Called for the change of a pre-existing branch
	#
	generate_update_branch_email()
	{
	# Consider this:
	# 1 --- 2 --- O --- X --- 3 --- 4 --- N
	#
	# O is $oldrev for $refname
	# N is $newrev for $refname
	# X is a revision pointed to by some other ref, for which we may
	# assume that an email has already been generated.
	# In this case we want to issue an email containing only revisions
	# 3, 4, and N. Given (almost) by
	#
	# git rev-list N ^O --not --all
	#
	# The reason for the "almost", is that the "--not --all" will take
	# precedence over the "N", and effectively will translate to
	#
	# git rev-list N ^O ^X ^N
	#
	# So, we need to build up the list more carefully. git rev-parse
	# will generate a list of revs that may be fed into git rev-list.
	# We can get it to make the "--not --all" part and then filter out
	# the "^N" with:
	#
	# git rev-parse --not --all \| grep -v N
	#
	# Then, using the --stdin switch to git rev-list we have effectively
	# manufactured
	#
	# git rev-list N ^O ^X
	#
	# This leaves a problem when someone else updates the repository
	# while this script is running. Their new value of the ref we're
	# working on would be included in the "--not --all" output; and as
	# our $newrev would be an ancestor of that commit, it would exclude
	# all of our commits. What we really want is to exclude the current
	# value of $refname from the --not list, rather than N itself. So:
	#
	# git rev-parse --not --all \| grep -v $(git rev-parse $refname)
	#
	# Get's us to something pretty safe (apart from the small time
	# between refname being read, and git rev-parse running - for that,
	# I give up)
	#
	#
	# Next problem, consider this:
	# * --- B --- * --- O ($oldrev)
	# \
	# * --- X --- * --- N ($newrev)
	#
	# That is to say, there is no guarantee that oldrev is a strict
	# subset of newrev (it would have required a --force, but that's
	# allowed). So, we can't simply say rev-list $oldrev..$newrev.
	# Instead we find the common base of the two revs and list from
	# there.
	#
	# As above, we need to take into account the presence of X; if
	# another branch is already in the repository and points at some of
	# the revisions that we are about to output - we don't want them.
	# The solution is as before: git rev-parse output filtered.
	#
	# Finally, tags: 1 --- 2 --- O --- T --- 3 --- 4 --- N
	#
	# Tags pushed into the repository generate nice shortlog emails that
	# summarise the commits between them and the previous tag. However,
	# those emails don't include the full commit messages that we output
	# for a branch update. Therefore we still want to output revisions
	# that have been output on a tag email.
	#
	# Luckily, git rev-parse includes just the tool. Instead of using
	# "--all" we use "--branches"; this has the added benefit that
	# "remotes/" will be ignored as well.

	# List all of the revisions that were removed by this update, in a
	# fast-forward update, this list will be empty, because rev-list O
	# ^N is empty. For a non-fast-forward, O ^N is the list of removed
	# revisions
	fast_forward=""
	rev=""
	for rev in $(git rev-list $newrev..$oldrev)
	do
	revtype=$(git cat-file -t "$rev")
	echo " discards $rev ($revtype)"
	done
	if [ -z "$rev" ]; then
	fast_forward=1
	fi

	# List all the revisions from baserev to newrev in a kind of
	# "table-of-contents"; note this list can include revisions that
	# have already had notification emails and is present to show the
	# full detail of the change from rolling back the old revision to
	# the base revision and then forward to the new revision
	for rev in $(git rev-list $oldrev..$newrev)
	do
	revtype=$(git cat-file -t "$rev")
	echo " via $rev ($revtype)"
	done

	if [ "$fast_forward" ]; then
	echo " from $oldrev ($oldrev_type)"
	else
	# 1. Existing revisions were removed. In this case newrev
	# is a subset of oldrev - this is the reverse of a
	# fast-forward, a rewind
	# 2. New revisions were added on top of an old revision,
	# this is a rewind and addition.

	# (1) certainly happened, (2) possibly. When (2) hasn't
	# happened, we set a flag to indicate that no log printout
	# is required.

	echo ""

	# Find the common ancestor of the old and new revisions and
	# compare it with newrev
	baserev=$(git merge-base $oldrev $newrev)
	rewind_only=""
	if [ "$baserev" = "$newrev" ]; then
	echo "This update discarded existing revisions and left the branch pointing at"
	echo "a previous point in the repository history."
	echo ""
	echo " * -- * -- N ($newrev)"
	echo " \\"
	echo " O -- O -- O ($oldrev)"
	echo ""
	echo "The removed revisions are not necessarily gone - if another reference"
	echo "still refers to them they will stay in the repository."
	rewind_only=1
	else
	echo "This update added new revisions after undoing existing revisions. That is"
	echo "to say, the old revision is not a strict subset of the new revision. This"
	echo "situation occurs when you --force push a change and generate a repository"
	echo "containing something like this:"
	echo ""
	echo " * -- * -- B -- O -- O -- O ($oldrev)"
	echo " \\"
	echo " N -- N -- N ($newrev)"
	echo ""
	echo "When this happens we assume that you've already had alert emails for all"
	echo "of the O revisions, and so we here report only the revisions in the N"
	echo "branch from the common base, B."
	fi
	fi

	echo ""
	if [ -z "$rewind_only" ]; then
	echo "Those revisions listed above that are new to this repository have"
	echo "not appeared on any other notification email; so we list those"
	echo "revisions in full, below."

	echo ""
	echo $LOGBEGIN
	show_new_revisions

	# XXX: Need a way of detecting whether git rev-list actually
	# outputted anything, so that we can issue a "no new
	# revisions added by this update" message

	echo $LOGEND
	else
	echo "No new revisions were added by this update."
	fi

	# The diffstat is shown from the old revision to the new revision.
	# This is to show the truth of what happened in this change.
	# There's no point showing the stat from the base to the new
	# revision because the base is effectively a random revision at this
	# point - the user will be interested in what this revision changed
	# - including the undoing of previous revisions in the case of
	# non-fast-forward updates.
	echo ""
	echo "Summary of changes:"
	git diff-tree $diffopts $oldrev..$newrev
	}

	#
	# Called for the deletion of a branch
	#
	generate_delete_branch_email()
	{
	echo " was $oldrev"
	echo ""
	echo $LOGBEGIN
	git show -s --pretty=oneline $oldrev
	echo $LOGEND
	}

	# --------------- Annotated tags

	#
	# Called for the creation of an annotated tag
	#
	generate_create_atag_email()
	{
	echo " at $newrev ($newrev_type)"

	generate_atag_email
	}

	#
	# Called for the update of an annotated tag (this is probably a rare event
	# and may not even be allowed)
	#
	generate_update_atag_email()
	{
	echo " to $newrev ($newrev_type)"
	echo " from $oldrev (which is now obsolete)"

	generate_atag_email
	}

	#
	# Called when an annotated tag is created or changed
	#
	generate_atag_email()
	{
	# Use git for-each-ref to pull out the individual fields from the
	# tag
	eval $(git for-each-ref --shell --format='
	tagobject=%(*objectname)
	tagtype=%(*objecttype)
	tagger=%(taggername)
	tagged=%(taggerdate)' $refname
	)

	echo " tagging $tagobject ($tagtype)"
	case "$tagtype" in
	commit)

	# If the tagged object is a commit, then we assume this is a
	# release, and so we calculate which tag this tag is
	# replacing
	prevtag=$(git describe --abbrev=0 $newrev^ 2>/dev/null)

	if [ -n "$prevtag" ]; then
	echo " replaces $prevtag"
	fi
	;;
	*)
	echo " length $(git cat-file -s $tagobject) bytes"
	;;
	esac
	echo " tagged by $tagger"
	echo " on $tagged"

	echo ""
	echo $LOGBEGIN

	# Show the content of the tag message; this might contain a change
	# log or release notes so is worth displaying.
	git cat-file tag $newrev \| sed -e '1,/^$/d'

	echo ""
	case "$tagtype" in
	commit)
	# Only commit tags make sense to have rev-list operations
	# performed on them
	if [ -n "$prevtag" ]; then
	# Show changes since the previous release
	git rev-list --pretty=short "$prevtag..$newrev" \| git shortlog
	else
	# No previous tag, show all the changes since time
	# began
	git rev-list --pretty=short $newrev \| git shortlog
	fi
	;;
	*)
	# XXX: Is there anything useful we can do for non-commit
	# objects?
	;;
	esac

	echo $LOGEND
	}

	#
	# Called for the deletion of an annotated tag
	#
	generate_delete_atag_email()
	{
	echo " was $oldrev"
	echo ""
	echo $LOGBEGIN
	git show -s --pretty=oneline $oldrev
	echo $LOGEND
	}

	# --------------- General references

	#
	# Called when any other type of reference is created (most likely a
	# non-annotated tag)
	#
	generate_create_general_email()
	{
	echo " at $newrev ($newrev_type)"

	generate_general_email
	}

	#
	# Called when any other type of reference is updated (most likely a
	# non-annotated tag)
	#
	generate_update_general_email()
	{
	echo " to $newrev ($newrev_type)"
	echo " from $oldrev"

	generate_general_email
	}

	#
	# Called for creation or update of any other type of reference
	#
	generate_general_email()
	{
	# Unannotated tags are more about marking a point than releasing a
	# version; therefore we don't do the shortlog summary that we do for
	# annotated tags above - we simply show that the point has been
	# marked, and print the log message for the marked point for
	# reference purposes
	#
	# Note this section also catches any other reference type (although
	# there aren't any) and deals with them in the same way.

	echo ""
	if [ "$newrev_type" = "commit" ]; then
	echo $LOGBEGIN
	git show --no-color --root -s --pretty=medium $newrev
	echo $LOGEND
	else
	# What can we do here? The tag marks an object that is not
	# a commit, so there is no log for us to display. It's
	# probably not wise to output git cat-file as it could be a
	# binary blob. We'll just say how big it is
	echo "$newrev is a $newrev_type, and is $(git cat-file -s $newrev) bytes long."
	fi
	}

	#
	# Called for the deletion of any other type of reference
	#
	generate_delete_general_email()
	{
	echo " was $oldrev"
	echo ""
	echo $LOGBEGIN
	git show -s --pretty=oneline $oldrev
	echo $LOGEND
	}


	# --------------- Miscellaneous utilities

	#
	# Show new revisions as the user would like to see them in the email.
	#
	show_new_revisions()
	{
	# This shows all log entries that are not already covered by
	# another ref - i.e. commits that are now accessible from this
	# ref that were previously not accessible
	# (see generate_update_branch_email for the explanation of this
	# command)

	# Revision range passed to rev-list differs for new vs. updated
	# branches.
	if [ "$change_type" = create ]
	then
	# Show all revisions exclusive to this (new) branch.
	revspec=$newrev
	else
	# Branch update; show revisions not part of $oldrev.
	revspec=$oldrev..$newrev
	fi

	other_branches=$(git for-each-ref --format='%(refname)' refs/heads/ \|
	grep -F -v $refname)
	git rev-parse --not $other_branches \|
	if [ -z "$custom_showrev" ]
	then
	git rev-list --pretty --stdin $revspec
	else
	git rev-list --stdin $revspec \|
	while read onerev
	do
	eval $(printf "$custom_showrev" $onerev)
	done
	fi
	}


	limit_lines()
	{
	lines=0
	skipped=0
	while IFS="" read -r line; do
	lines=$((lines + 1))
	if [ $lines -gt $1 ]; then
	skipped=$((skipped + 1))
	else
	printf "%s\n" "$line"
	fi
	done
	if [ $skipped -ne 0 ]; then
	echo "... $skipped lines suppressed ..."
	fi
	}


	send_mail()
	{
	if [ -n "$envelopesender" ]; then
	/usr/sbin/sendmail -t -f "$envelopesender"
	else
	/usr/sbin/sendmail -t
	fi
	}

	# ---------------------------- main()

	# --- Constants
	LOGBEGIN="- Log -----------------------------------------------------------------"
	LOGEND="-----------------------------------------------------------------------"

	# --- Config
	# Set GIT_DIR either from the working directory, or from the environment
	# variable.
	GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
	if [ -z "$GIT_DIR" ]; then
	echo >&2 "fatal: post-receive: GIT_DIR not set"
	exit 1
	fi

	projectdesc=$(sed -ne '1p' "$GIT_DIR/description" 2>/dev/null)
	# Check if the description is unchanged from it's default, and shorten it to
	# a more manageable length if it is
	if expr "$projectdesc" : "Unnamed repository.*$" >/dev/null
	then
	projectdesc="UNNAMED PROJECT"
	fi

	recipients=$(git config hooks.mailinglist)
	announcerecipients=$(git config hooks.announcelist)
	envelopesender=$(git config hooks.envelopesender)
	emailprefix=$(git config hooks.emailprefix \|\| echo '[SCM] ')
	custom_showrev=$(git config hooks.showrev)
	maxlines=$(git config hooks.emailmaxlines)
	diffopts=$(git config hooks.diffopts)
	: ${diffopts:="--stat --summary --find-copies-harder"}

	# --- Main loop
	# Allow dual mode: run from the command line just like the update hook, or
	# if no arguments are given then run as a hook script
	if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
	# Output to the terminal in command line mode - if someone wanted to
	# resend an email; they could redirect the output to sendmail
	# themselves
	prep_for_email $2 $3 $1 && PAGER= generate_email
	else
	while read oldrev newrev refname
	do
	prep_for_email $oldrev $newrev $refname \|\| continue
	generate_email $maxlines \| send_mail
	done
	fi