[PATCH 3/4] update-hook: parse the tag header in preparation to use the tag type

[Andy Parkins <andyparkins@gmail.com>]

The tag header is parsed with a while loop and read command.  I'm not
entirely sure how portable it is, as it had to use the following unusual
heredoc format:

  while read field value
  do
    # ..
  done <<< "$(some command)"

This was necessary because piping the output to a while doesn't work
because the pipe is run in a separate process and hence setting
variables inside it has no effect in the main script process.  This
"<<<" heredoc notation works around that problem, but I have no idea how
widely supported it is.  The alternative (should it be necessary) is
to wastefully make multiple "git-cat-file | sed" calls - yuck.

This patch also updates the user/time extraction from the "tagger" field
to use the variable $tagger, rather than the "git-cat-file | sed" call
used previously.

Signed-off-by: Andy Parkins <andyparkins@gmail.com>
---
 templates/hooks--update |   24 +++++++++++++++++++++---
 1 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/templates/hooks--update b/templates/hooks--update
index 31e72ca..fd4c081 100644
--- a/templates/hooks--update
+++ b/templates/hooks--update
@@ -215,15 +215,33 @@ case "$refname_type" in
 			echo "      from  $oldrev"
 		fi
 
+		# Read the tag header
+		while read field value
+		do
+			case "$field" in
+			object)
+				tagobject="$value"
+				;;
+			type)
+				tagtype="$value"
+				;;
+			tag)
+				# Confirm that this tag has the right name?  Nah
+				;;
+			tagger)
+				tagger="$value"
+				;;
+			esac
+		done <<< "$(git cat-file tag $newrev | head -q -n 4)"
+
 		# If this tag succeeds another, then show which tag it replaces
 		prevtag=$(git describe --abbrev=0 $newrev^ 2>/dev/null)
 		if [ -n "$prevtag" ]; then
 			echo "  replaces  $prevtag"
 		fi
 
-		# Read the tag details
-		eval $(git cat-file tag $newrev | \
-			sed -n '4s/tagger \([^>]*>\)[^0-9]*\([0-9]*\).*/tagger="\1" ts="\2"/p')
+		# Extract user and time from tagger variable
+		eval $(sed -n 's/\([^>]*>\)[^0-9]*\([0-9]*\).*/tagger="\1" ts="\2"/p' <<< "$tagger")
 		tagged=$(date --date="1970-01-01 00:00:00 +0000 $ts seconds" +"$DATEFORMAT")
 
 		echo " tagged by  $tagger"
-- 
1.5.0.3.402.g0c48