Using the Commit Templates feature in Mercurial

Mercurial supports setting the changeset option in the comittemplate section of your hgrc file to be the commit description. This can be used to pre-populate empty commit messages, and can include things like showing the diffs that are about to be committed. See hg help config.committemplate for full information on this feature.

Using a separate program

Mercurial calls a user-defined program to edit commit messages. If that program returns false, the commit is aborted.

Here's an example patch for hgeditor that adds a user-defined template to the commit message:

diff -r 33988aaa1652 hgeditor
--- a/hgeditor Sun Dec 17 22:16:57 2006 -0600
+++ b/hgeditor Tue Dec 19 08:08:57 2006 -0600
@@ -39,6 +39,7 @@ HGTMP="${TMPDIR-/tmp}/hgeditor.$RANDOM.$

-cat "$1" > "$HGTMP/msg"
+cat `hg root`/.commit-template > "$HGTMP/msg"
+cat "$1" >> "$HGTMP/msg"

 MD5=$(which md5sum 2>/dev/null) || \

Validating that the commit message is correct can either be done by hgeditor or enforced by a precommit hook.

Another way

The following pair of scripts respects the user's chosen editor.

A usage scenario is a repository with main branch being the "default" branch. Users create named side branches, and when work is done (including code review), they merge to the default branch and push to the central repository. Users call "hg_commit_default" to ensure that the merge commit goes to the default branch (it is not hard to make a mistake), and are presented with a commit template that contains the recommended fields. Users may elect to delete some fields if they don't apply - the template is not enforced.

Script hg_commit_default:

# Commit to default branch.
# Ensure that branch is default.
# Provide commit message template.
# TODO: Disallow commit message passed with -m or -l.
#   Perhaps include it in the template?

BRANCH=`hg branch` || exit $?

if [ "$BRANCH" != default ] ; then
    echo "Branch $BRANCH is not default branch" >&2
    exit 1

# Save the value to be overridden

HGEDITOR=hg_templated_editor exec hg commit "$@"

Script hg_templated_editor:

# Called by hg_commit_default.
# Calls configured commit editor with a template commit message.


HG_CONF_EDITOR=`hg showconfig ui.editor`

if [ "$HGEDITOR_ORIG" ] ; then
elif [ "$HG_CONF_EDITOR" ] ; then
elif [ "$VISUAL" ] ; then
elif [ "$EDITOR" ] ; then

cleanup_exit() {
    /bin/rm -f "$TMP"

# Cleanup temporary file on exit or abnormal interruption
trap "cleanup_exit" 0 # normal exit
trap "exit 255" 1 2 3 6 15 # HUP INT QUIT ABRT TERM

# $TMP should match the permissions of $FILE
umask 077

# Prepend the custom template. The first line is empty.
echo "" > "$TMP" || exit $?
echo "Bug: " >> "$TMP"
echo "Reviewer: " >> "$TMP"
echo "Tests: " >> "$TMP"

# Append the original template.
# grep removes the first empty line.
grep -v '^$' "$FILE" >> "$TMP"

CHECKSUM=`md5sum "$TMP"`

$ED "$TMP" || exit $?

# Detect if no change was made to the commit message
echo "$CHECKSUM" | md5sum -c --status && exit 0
# On exit 0 original $FILE remains unchanged and hg will complain about that.

/bin/mv "$TMP" "$FILE"


CommitMessageTemplate (last edited 2019-05-08 01:49:37 by KyleLippincott)