The GCC checkin policy requires a ChangeLog entry for each change, and that entry is usually also used as the commit message. I used to use a fairly crappy, homemade vim plugin to extract the first entry from a ChangeLog file into the editor buffer to use as the svn commit message. I decided to replace that vim plugin with a Git prepate-commit-msg hook that automatically prepares the commit message for me by extracting the first entry from each ChangeLog that is part of the commit.

As a cursory web search didn't find anything similar, I'm posting it here in case it's useful to anyone else.

$ cat .git/hooks/prepare-commit-msg

#!/bin/bash

#

# Hook script to prepare the commit log message from the first

# entry in each modified ChangeLog being committed.


set -e


[[ "$2,$3" == 'merge,' ]] && exit


tmpf=$(mktemp)

awk -f $0.awk $(git status -s | awk '/^M .*ChangeLog/{print $NF}') > $tmpf

sed 1d $1 >> $tmpf

mv $tmpf $1

$ cat .git/hooks/prepare-commit-msg.awk

# When there is more than one ChangeLog in the commit, precede

# the entry by the directory name.

FNR == 1 && ARGC > 2 {

  printf "%s:\n\n", gensub("/ChangeLog$", "", "", FILENAME)

}


# Save the first line until we know if we want to print it.

FNR == 1 {

  line1=$0

}


# If second line is blank there is only one patch author, omit it.

FNR == 2 && /^$/ {

}


# If second line is not blank there are multiple authors, print them.

FNR == 2 && /^./ {

  print line1

  print

}


# Stop processing the file at the next entry.

FNR > 3 && /^20[1-9][0-9]-[0-1][1-9]-[0-3][0-9]  / {

  nextfile

}


# Otherwise, just print the line.

FNR > 2 {

  print

}