diff --git a/git_helpers b/git_helpers
new file mode 100755
index 0000000..1343269
--- /dev/null
+++ b/git_helpers
@@ -0,0 +1,241 @@
+#!/bin/bash
+# set -x 
+
+source ./log_helpers.sh
+
+GIT_SSL_NO_VERIFY=true
+
+#
+exec_git_command () {
+    local func="${FUNCNAME[0]}"
+    
+    log_debug "$func:${LINENO} exec-ing $1"
+
+    exec {fd}< <($1)
+    local ps_pid=$!             # remember pid of process substitution
+
+    local git_result=""
+    while read t <&$fd; do
+        if ! [ -z "$t" ]; then
+            git_result="${git_result}$t"
+        fi
+    done
+        
+    exec {fd}>&-                # close fd (i.e. process substitution)
+    wait $ps_pid                # wait for the subshell to finish
+
+    git_result=$(printf "$git_result" | tr '\n' ' ')
+    printf "%s\n" $git_result
+}
+
+# 
+latest_commit () {
+    local func="${FUNCNAME[0]}"
+    # git reflog -> 46c5896 HEAD@{0}: commit: Made update_helpers.sh executable
+    local c=$(git reflog | grep "HEAD@{0}" | cut -d" " -f1)
+    if ! [ -z "$c" ]; then
+        if grep -qE "^[[:xdigit:]]{6,}$" <<< $c; then
+            log_debug "$func: commit -> $c"
+            printf "%s\n" $c
+        else
+            log_crit "$func: wrong format for commit c=$c"
+            printf ""
+        fi
+    else 
+        log_crit "$func: 'git reflog' result empty"
+        printf ""
+    fi
+}
+
+# fallback if something went wrong: revert to last valid commit
+revert_to_commit_before_pull () {
+    local func="${FUNCNAME[0]}"
+    if ! [ -z "$commit_before_pull" ]; then
+        if grep -qE "^[[:xdigit:]]{6,}$" <<< $commit_before_pull; then
+            `git reset --hard "$commit_before_pull"`
+            if [ $? -eq 0 ]; then
+                log_info "$func: git reset --hard $commit_before_pull"
+                return 0
+            fi
+            log_crit "$func: 'git reset --hard $commit_before_pull' failed!"
+        fi
+        log_crit "$func: wrong format for commit_before_pull"
+    fi
+    log_crit "$func: empty commit_before_pull"
+    return 1
+}
+# revert_to_commit_before_pull
+
+# clone the customer repository in ./UpdateController/workspace.
+# this is done only once.
+clone_customer_repository () {
+    local func="${FUNCNAME[0]}"
+    current_dir=${PWD##*/}
+    current_dir="./${current_dir:-/}"
+    if [ "$current_dir" = "./UpdateController" ]; then
+        if ! [[ -d ./workspace ]]; then
+            { mkdir -p ./workspace; }
+        fi
+        # check if the directory is empty. If so, clone the
+        # customer repository
+        if ! find ./workspace -mindepth 1 -maxdepth 1 | read; then
+            log_debug "$func: cloning ${1} ..."
+            ( cd ./workspace && git clone "$1" ; )
+            if [ $? -eq 0 ]; then
+                log_debug "$func: cloning ${1} done"
+                return 0
+            fi
+        fi
+    fi
+    return 1
+}
+# clone_customer_repository ->
+# https://git.mimbach49.de/GerhardHoffmann/customer_281.git
+
+cd_customer_repository () {
+    # has to be called in ./UpdateController
+    local func="${FUNCNAME[0]}"
+    current_dir=${PWD##*/}
+    current_dir="./${current_dir:-/}"
+    if [ "$current_dir" = "./UpdateController" ]; then
+        repository_dir="./workspace/${customer_id}"
+        if ! [[ -d "$repository_dir" ]]; then
+            log_crit "$func:${LINENO}: $repository_dir does not exist!"
+            return 1
+        fi
+        
+        if ! cd $repository_dir; then
+            log_crit "$func:${LINENO}: cannot change to $repository_dir!"
+            return 1
+        fi
+
+        log_debug "$func:${LINENO}: cd to $repository_dir!"
+        return 0
+    fi
+    return 1
+}
+
+cd_home () {
+    if cd - &>/dev/null ; then
+        return 0
+    fi
+    return 1
+}
+
+pull_customer_repository () {
+    # has to be called in ./UpdateController
+    local func="${FUNCNAME[0]}"
+
+    if ! cd_customer_repository ; then
+        return 1
+    fi
+
+    local commit_before_pull=$(latest_commit)
+    if [ -z $commit_before_pull ]; then
+        cd_home ; return 1
+    fi
+
+    log_debug "$func:${LINENO}: commit_before_pull=$commit_before_pull"
+
+    exec {fd}< <(git pull)
+    local ps_pid=$!             # remember pid of process substitution
+
+    local git_result=""
+    while read t <&$fd; do
+        if ! [ -z "$t" ]; then
+            git_result="${git_result}$t"
+        fi
+    done
+        
+    exec {fd}>&-                # close fd (i.e. process substitution)
+    wait $ps_pid                # wait for the subshell to finish
+
+    if [ -z "$git_result" ]; then
+        log_warn "$func:${LINENO}: git result empty" ; cd_home;
+        return 1
+    fi
+
+    log_debug "$func:${LINENO} git-pull-result=${git_result}"
+
+    if [ "$git_result" = "Already up to date." ]; then
+        log_warn "$func:${LINENO}: $PWD already up to date."
+        cd_home ; return 1
+    fi
+
+    local commit_after_pull=$(latest_commit)
+    if [ -z $commit_after_pull ]; then
+        cd_home ; return 1
+    fi
+        
+    log_debug "$func:${LINENO}: commit_after_pull=$commit_after_pull"
+
+    # Note: # 'git pull' is a 'git fetch' followed by a 'git merge'.
+    # Here's the fetch portion:
+    #
+    # remote: Counting objects: 11, done.
+    # remote: Compressing objects: 100% (5/5), done.
+    # remote: Total 7 (delta 2), reused 0 (delta 0)
+    #
+    # At this point, you've told the remote what you want.
+    # It finds all the objects it needs to give you,
+    # compresses them for faster transfer over the network,
+    # and then reports what it's sending you.
+    # 
+    # Unpacking objects: 100% (7/7), done.
+    # 
+    # You receive the pack (set of compressed objects) and unpack it.
+    #
+    # From ssh://my.remote.host.com/~/git/myproject
+    # * branch            master     -> FETCH_HEAD
+
+    # You've fetched the branch 'master' from the given remote;
+    # the ref FETCH_HEAD now points to it.
+    # Now we move on to the merge - precisely, git will merge
+    # FETCH_HEAD (the remote's master branch) into your current branch
+    # (presumably master).
+    #
+    #######################################################################
+    # here starts "message"
+    # 
+    # Updating 9d447d2..f74fb21
+    # Fast forward
+    #
+    # It turns out that you haven't diverged from the remote's master branch,
+    # so the merge is a fast-forward (a trivial merge where it simply moves
+    # you forward in the history).
+    #
+    # Git notes the original position of your master branch (9d447d2)
+    # and the new position (f74fb21) it's been fast-forwarded to.
+    # If you had diverged from the remote's master branch,
+    # you'd see the output of a recursive merge here - Merge made
+    # by recursive, possibly along with some Auto-merged <file>
+    # and (oh no!) merge conflicts!
+    #
+    # szeged/1/1/etc/psa_config/device.conf | 13 +++++++------
+    # szeged/update.conf                    |  2 +-
+    # 2 files changed, 8 insertions(+), 7 deletions(-)
+    #  
+    # Finally, it shows you the diffstat between the original and post-merge
+    # position of your master branch;
+    # this is basically what you'd get from
+    #
+    # git diff --stat master@{1} master.
+    # 
+
+    update_commit="${commit_before_pull}..${commit_after_pull}"
+    if ! grep -qE ".*Updating\s+${update_commit}.*?" <<< $git_result; then
+        log_crit "$func:${LINENO}: no $update_commit in [ $git_result ]"
+        cd_home ; return 1
+    fi
+
+    return 0
+}
+# pull_customer_repository customer_281
+
+changed_files () {
+    local func="${FUNCNAME[0]}"
+    if  cd_customer_repository ; then
+        printf "%s\n" $(exec_git_command 'git diff --stat master@{1} master')
+        cd_home
+    fi
+}