git hook to update composer dependencies only if changed, and to put the current revision in a file

post-checkout

#!/bin/bash
#set -x
githooks/post-checkout-revision.sh
githooks/post-checkout-composer.sh

post-checkout-composer.sh

#!/bin/bash
OLD=`md5 -q composer.lock.old`
NEW=`md5 -q composer.lock`
if [ "$NEW" != "$OLD" ]
then
  rm -rf vendor
  php composer.phar install
fi
cat composer.lock > composer.lock.old

post-checkout-revision.sh

#!/bin/bash
b=$(git rev-parse --show-toplevel)
output_file=$b/docroot/www/revision.txt
branch=`git rev-parse --abbrev-ref HEAD `
revision=`git rev-parse HEAD`
echo -e "$branch $revision \n" > $output_file
current_date=`date +%A\ %F\ %r`
echo "Checkout at:$current_date" >>$output_file
last_commit_at=`git log -1 HEAD  --date=local --decorate --pretty=format:"%cd"`
echo "Last commit at: $last_commit_at " >>$output_file

you should add the composer.lock to the repo and add composer.lock.old to the .gitignore.
When you want to manually do an update, just run composer update and the commit the lock file.

referenced http://stackoverflow.com/questions/26930816/how-to-remove-unused-dependencies-from-composer/28558577