update-hook: parse the tag header in preparation to use the tag type

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.

---
 templates/hooks--update |   24 +++++++++++++++++++++---
 1 files changed, 21 insertions(+), 3 deletions(-)

index 31e72ca..fd4c081 100644
@@ -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

To bad you can't use for-each-ref. ;-)

The problem of course is the update hook is running before a ref is created to point at the tag. If you used post-receive hook on the other hand... Oh, right, that has its own problems too!

Shawn.

I've obviously not described the problem very well; as I don't understand how your comment relates to this patch.

All I'm doing is pulling the individual fields out of

 $ git cat-file -p v1.5.0
 object 437b1b20df4b356c9342dac8d38849f24ef44f27
 type commit
 tag v1.5.0
 tagger Junio C Hamano <[email protected]> Wed Feb 14 00:00:00 2007 +0000

And putting them in their own variables. I'm not sure how for-each-ref or in fact, any ref-based tool would help me do this. At this point it's nothing to do with git, it's a standard shell script problem.

git cat-file -p $newrev | while read field value
do
variable = "found"
done
echo $variable

Doesn't work, because the right half of the pipe is run in its own process and so setting "variable" has no effect once the while loop is over.

I found that "<<<" heredoc thing in the bash manual, which is almost like having a reverse pipe and allows the while loop to run in the main process.

Andy

Dr Andy Parkins, M Eng (hons), MIET
[email protected]

eval git for-each-ref --format='taggername=%(taggername) taggerdate=%(taggerdate)' thetag

Then you have $taggername and $taggerdate available. ;-)

The problem is, there is no ref to for-each over. :-(

Shawn.