diff --git a/Makefile b/Makefile
index 11b0b9d..1da3fa1 100644
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,8 @@
 SCRIPT_FILES+=git-flow-release
 SCRIPT_FILES+=git-flow-support
 SCRIPT_FILES+=git-flow-version
-SCRIPT_FILES+=shFlags.sh
+SCRIPT_FILES+=gitflow-common
+SCRIPT_FILES+=gitflow-shFlags
 
 all:
 	@echo "usage: make install"
diff --git a/git-flow b/git-flow
index f7a826d..573aa25 100755
--- a/git-flow
+++ b/git-flow
@@ -18,21 +18,13 @@
 	set -x
 fi
 
-export GIT_DIR=$(git rev-parse --git-dir)
 export GITFLOW_DIR=$(dirname "$0")
+export GIT_DIR=$(git rev-parse --git-dir)
 export MASTER_BRANCH=$(git config --get gitflow.branch.master || echo master)
 export DEVELOP_BRANCH=$(git config --get gitflow.branch.develop || echo develop)
 export ORIGIN=$(git config --get gitflow.origin || echo origin)
 export README=$(git config --get gitflow.readme || echo README)
 
-warn() { echo "$@" >&2; }
-die() { warn "$@"; exit 1; }
-
-has() {
-	local item=$1; shift
-	echo " $@ " | grep -q " $item "
-}
-
 usage() {
 	echo "usage: git flow <subcommand>"
 	echo
@@ -53,11 +45,12 @@
 		exit 1
 	fi
 
+	# load common functionality
+	. "$GITFLOW_DIR/gitflow-common"
+
 	# use the shFlags project to parse the command line arguments
-	. "$GITFLOW_DIR/shFlags.sh"
+	. "$GITFLOW_DIR/gitflow-shFlags"
 	FLAGS_PARENT="git flow"
-	#DEFINE_boolean quiet 0 'run without output' q
-	#DEFINE_boolean verbose 0 'run verbose (more output)' v
 	FLAGS "$@" || exit $?
 	eval set -- "${FLAGS_ARGV}"
 
@@ -73,11 +66,6 @@
 		die "Not a git repository"
 	fi
 
-	# get all available branches
-	LOCAL_BRANCHES=$(git branch | sed 's/^[* ] //')
-	REMOTE_BRANCHES=$(git branch -r | sed 's/^[* ] //')
-	ALL_BRANCHES="$LOCAL_BRANCHES $REMOTE_BRANCHES"
-
 	# run command
 	. "$GITFLOW_DIR/git-flow-$SUBCOMMAND"
 	FLAGS_PARENT="git flow $SUBCOMMAND"
@@ -99,109 +87,6 @@
 	cmd_$SUBACTION "$@"
 }
 
-gitflow_test_clean_working_tree() {
-	if ! git diff --no-ext-diff --ignore-submodules --quiet --exit-code; then
-		return 1
-	elif ! git diff-index --cached --quiet --ignore-submodules HEAD --; then
-		return 2
-	else
-		return 0
-	fi
-}
-
-gitflow_require_clean_working_tree() {
-	gitflow_test_clean_working_tree
-	result=$?
-	if [ $result -eq 1 ]; then
-		die "fatal: Working tree contains unstaged changes. Aborting."
-	fi
-	if [ $result -eq 2 ]; then
-		die "fatal: Index contains uncommited changes. Aborting."
-	fi
-}
-
-gitflow_require_local_branch() {
-	if ! has $1 $LOCAL_BRANCHES; then
-		die "fatal: Local branch '$1' does not exist and is required."
-	fi
-}
-
-gitflow_require_remote_branch() {
-	if ! has $1 $REMOTE_BRANCHES; then
-		die "Remote branch '$1' does not exist and is required."
-	fi
-}
-
-gitflow_require_branch() {
-	if ! has $1 $ALL_BRANCHES; then
-		die "Branch '$1' does not exist and is required."
-	fi
-}
-
-gitflow_require_branch_absent() {
-	if has $1 $ALL_BRANCHES; then
-		die "Branch '$1' already exists. Pick another name."
-	fi
-}
-
-#
-# gitflow_test_branches_equal()
-#
-# Tests whether branches and their "origin" counterparts have diverged and need
-# merging first. It returns error codes to provide more detail, like so:
-#
-# 0    Branch heads point to the same commit
-# 1    First given branch needs fast-forwarding
-# 2    Second given branch needs fast-forwarding
-# 3    Branch needs a real merge
-#
-gitflow_test_branches_equal() {
-	commit1=$(git rev-parse "$1")
-	commit2=$(git rev-parse "$2")
-	if [ "$commit1" != "$commit2" ]; then
-		base=$(git merge-base "$commit1" "$commit2")
-		if [ "$commit1" = "$base" ]; then
-			return 1
-		elif [ "$commit2" = "$base" ]; then
-			return 2
-		else
-			return 3
-		fi
-	else
-		return 0
-	fi
-}
-
-gitflow_require_branches_equal() {
-	gitflow_require_local_branch "$1"
-	gitflow_require_remote_branch "$2"
-	gitflow_test_branches_equal "$1" "$2"
-	status=$?
-	if [ $status -gt 0 ]; then
-		warn "Branches '$1' and '$2' have diverged."
-		if [ $status -eq 1 ]; then
-			die "And branch '$1' may be fast-forwarded."
-		elif [ $status -eq 2 ]; then
-			# Warn here, since there is no harm in being ahead
-			warn "And local branch '$1' is ahead of '$2'."
-		else
-			die "Branches need merging first."
-		fi
-	fi
-}
-
-#
-# gitflow_is_branch_merged_into()
-#
-# Checks whether branch $1 is succesfully merged into $2
-#
-gitflow_is_branch_merged_into() {
-	local SUBJECT=$1
-	local BASE=$2
-	ALL_MERGES=$(git branch --contains $SUBJECT | sed 's/^[* ] //')
-	has $BASE $ALL_MERGES
-}
-
 # helper functions for common reuse
 max() { if [ "$1" -gt "$2" ]; then echo "$1"; else echo "$2"; fi; }
 
diff --git a/git-flow-feature b/git-flow-feature
index 33dab30..f25ae7f 100644
--- a/git-flow-feature
+++ b/git-flow-feature
@@ -32,28 +32,33 @@
 	DEFINE_boolean verbose false 'verbose (more) output' v
 	parse_args "$@"
 
-	FEATURE_BRANCHES="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
-	if [ -z "$FEATURE_BRANCHES" ]; then
+	typeset feature_branches
+	typeset current_branch
+	typeset short_names
+	feature_branches="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
+	if [ -z "$feature_branches" ]; then
 		warn "No feature branches exist."
 		exit 0
 	fi
+	current_branch=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
+	short_names=$(echo "$feature_branches" | sed "s ^$PREFIX  g")
 
-	CURRENT_BRANCH=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
-	SHORT_NAMES=$(echo "$FEATURE_BRANCHES" | sed "s?^$PREFIX??g")
 	# determine column width first
-	width=0
-	for branch in $SHORT_NAMES; do
-		len=$(($(echo "$branch" | wc -c) - 1))
+	typeset -i width=0
+	typeset branch
+	for branch in $short_names; do
+		typeset -i len=${#branch}
 		width=$(max $width $len)
 	done
-	width=$(($width + 3))
+	width=width+3
 
-	for branch in $SHORT_NAMES; do
-		fullname="$PREFIX$branch"
-		base=$(git merge-base "$fullname" "$DEVELOP_BRANCH")
-		develop_sha=$(git rev-parse "$DEVELOP_BRANCH")
-		branch_sha=$(git rev-parse "$fullname")
-		if [ "$fullname" = "$CURRENT_BRANCH" ]; then
+	typeset branch
+	for branch in $short_names; do
+		typeset fullname="$PREFIX$branch"
+		typeset base=$(git merge-base "$fullname" "$DEVELOP_BRANCH")
+		typeset develop_sha=$(git rev-parse "$DEVELOP_BRANCH")
+		typeset branch_sha=$(git rev-parse "$fullname")
+		if [ "$fullname" = "$current_branch" ]; then
 			printf "* "
 		else
 			printf "  "
@@ -82,26 +87,27 @@
 }
 
 resolve_name_by_prefix() {
+	typeset matches
+	typeset -i num_matches
+
 	# first, check if there is a perfect match
 	if has "$LOCAL_BRANCHES" "$PREFIX$1"; then
 		echo "$1"
 		return 0
 	fi
 
-	MATCHES="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX$1")"
-	NUM_MATCHES=$(echo "$MATCHES" | wc -l)
-	if [ -z "$MATCHES" ]; then
+	matches="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX$1")"
+	num_matches=$(echo "$matches" | wc -l)
+	if [ -z "$matches" ]; then
 		# no prefix match, so take it literally
 		echo "$1"
 	else
-		if [ $NUM_MATCHES -eq 1 ]; then
-			# sed arg looks a bit weird, but $PREFIX should not contain spaces,
-			# so this one is safe
-			echo "$MATCHES" | sed "s $PREFIX  g"
+		if [ $num_matches -eq 1 ]; then
+			echo "${matches#$PREFIX}"
 		else
 			# multiple matches, cannot decide
 			warn "Multiple branches match for prefix '$1':"
-			for match in $MATCHES; do
+			for match in $matches; do
 				warn "- $match"
 			done
 			die "Aborting. Use an unambiguous prefix."
@@ -127,11 +133,11 @@
 }
 
 expand_name_arg_prefix_or_current() {
-	CURRENT_BRANCH=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
+	current_branch=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
 	if [ "$NAME" != "" ]; then
 		expand_name_arg_prefix
-	elif [ "$CURRENT_BRANCH" != "" ]; then
-		BRANCH="$CURRENT_BRANCH"
+	elif [ "$current_branch" != "" ]; then
+		BRANCH="$current_branch"
 		NAME=$(echo "$BRANCH" | sed "s?$PREFIX??g")
 	else
 		warn "The current HEAD is no feature branch."
@@ -364,8 +370,8 @@
 		BASE=$(git merge-base $DEVELOP_BRANCH $BRANCH)
 		git diff $BASE..$BRANCH
 	else
-		CURRENT_BRANCH=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
-		if ! echo "$CURRENT_BRANCH" | grep -q "^$PREFIX"; then
+		current_branch=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
+		if ! echo "$current_branch" | grep -q "^$PREFIX"; then
 			die "Not on a feature branch. Name one explicitly."
 		fi
 
@@ -383,7 +389,7 @@
 	gitflow_require_branch "$BRANCH"
 
 	git checkout -q "$BRANCH"
-	OPTS=
+	typeset OPTS=
 	if flag interactive; then
 		OPTS="$OPTS -i"
 	fi
diff --git a/git-flow-hotfix b/git-flow-hotfix
index efc69a7..35fed5b 100644
--- a/git-flow-hotfix
+++ b/git-flow-hotfix
@@ -30,28 +30,33 @@
 	DEFINE_boolean verbose false 'verbose (more) output' v
 	parse_args "$@"
 
-	HOTFIX_BRANCHES="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
-	if [ -z "$HOTFIX_BRANCHES" ]; then
+	typeset hotfix_branches
+	typeset current_branch
+	typeset short_names
+	hotfix_branches="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
+	if [ -z "$hotfix_branches" ]; then
 		warn "No hotfix branches exist."
 		exit 0
 	fi
+	current_branch=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
+	short_names=$(echo "$hotfix_branches" | sed "s?^$PREFIX??g")
 
-	CURRENT_BRANCH=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
-	SHORT_NAMES=$(echo "$HOTFIX_BRANCHES" | sed "s?^$PREFIX??g")
 	# determine column width first
-	width=0
-	for branch in $SHORT_NAMES; do
-		len=$(($(echo "$branch" | wc -c) - 1))
+	typeset -i width=0
+	typeset branch
+	for branch in $short_names; do
+		typeset -i len=$(($(echo "$branch" | wc -c) - 1))
 		width=$(max $width $len)
 	done
-	width=$(($width + 3))
+	width=width+3
 
-	for branch in $SHORT_NAMES; do
-		fullname="$PREFIX$branch"
-		base=$(git merge-base "$fullname" "$MASTER_BRANCH")
-		master_sha=$(git rev-parse "$MASTER_BRANCH")
-		branch_sha=$(git rev-parse "$fullname")
-		if [ "$fullname" = "$CURRENT_BRANCH" ]; then
+	typeset branch
+	for branch in $short_names; do
+		typeset fullname="$PREFIX$branch"
+		typeset base=$(git merge-base "$fullname" "$MASTER_BRANCH")
+		typeset master_sha=$(git rev-parse "$MASTER_BRANCH")
+		typeset branch_sha=$(git rev-parse "$fullname")
+		if [ "$fullname" = "$current_branch" ]; then
 			printf "* "
 		else
 			printf "  "
@@ -61,7 +66,8 @@
 			if [ "$branch_sha" = "$master_sha" ]; then
 				printf "(no commits yet)"
 			else
-				tagname=$(git name-rev --tags --no-undefined --name-only $base)
+				typeset tagname=$(git name-rev --tags --no-undefined --name-only $base)
+				typeset nicename
 				if [ "$tagname" != "" ]; then
 					nicename="$tagname"
 				else
diff --git a/git-flow-release b/git-flow-release
index b75891e..b23914e 100644
--- a/git-flow-release
+++ b/git-flow-release
@@ -41,28 +41,34 @@
 	DEFINE_boolean verbose false 'verbose (more) output' v
 	parse_args "$@"
 
-	RELEASE_BRANCHES="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
-	if [ -z "$RELEASE_BRANCHES" ]; then
+	typeset release_branches
+	typeset current_branch
+	typeset short_names
+	release_branches="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
+	if [ -z "$release_branches" ]; then
 		warn "No release branches exist."
 		exit 0
 	fi
 
-	CURRENT_BRANCH=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
-	SHORT_NAMES=$(echo "$RELEASE_BRANCHES" | sed "s?^$PREFIX??g")
+	current_branch=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
+	short_names=$(echo "$release_branches" | sed "s?^$PREFIX??g")
+
 	# determine column width first
-	width=0
-	for branch in $SHORT_NAMES; do
-		len=$(($(echo "$branch" | wc -c) - 1))
+	typeset -i width=0
+	typeset branch
+	for branch in $short_names; do
+		typeset -i len=$(($(echo "$branch" | wc -c) - 1))
 		width=$(max $width $len)
 	done
-	width=$(($width + 3))
+	width=width+3
 
-	for branch in $SHORT_NAMES; do
-		fullname="$PREFIX$branch"
-		base=$(git merge-base "$fullname" "$DEVELOP_BRANCH")
-		develop_sha=$(git rev-parse "$DEVELOP_BRANCH")
-		branch_sha=$(git rev-parse "$fullname")
-		if [ "$fullname" = "$CURRENT_BRANCH" ]; then
+	typeset branch
+	for branch in $short_names; do
+		typeset fullname="$PREFIX$branch"
+		typeset base=$(git merge-base "$fullname" "$DEVELOP_BRANCH")
+		typeset develop_sha=$(git rev-parse "$DEVELOP_BRANCH")
+		typeset branch_sha=$(git rev-parse "$fullname")
+		if [ "$fullname" = "$current_branch" ]; then
 			printf "* "
 		else
 			printf "  "
@@ -72,7 +78,7 @@
 			if [ "$branch_sha" = "$develop_sha" ]; then
 				printf "(no commits yet)"
 			else
-				nicename="$(git rev-parse --short $base)"
+				typeset nicename="$(git rev-parse --short $base)"
 				printf "(based on $nicename)"
 			fi
 		else
diff --git a/git-flow-support b/git-flow-support
index e334592..5dd07d8 100644
--- a/git-flow-support
+++ b/git-flow-support
@@ -32,28 +32,33 @@
 	DEFINE_boolean verbose false 'verbose (more) output' v
 	parse_args "$@"
 
-	SUPPORT_BRANCHES="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
-	if [ -z "$SUPPORT_BRANCHES" ]; then
+	typeset support_branches
+	typeset current_branch
+	typeset short_names
+	support_branches="$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")"
+	if [ -z "$support_branches" ]; then
 		warn "No support branches exist."
 		exit 0
 	fi
+	current_branch=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
+	short_names=$(echo "$support_branches" | sed "s?^$PREFIX??g")
 
-	CURRENT_BRANCH=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
-	SHORT_NAMES=$(echo "$SUPPORT_BRANCHES" | sed "s?^$PREFIX??g")
 	# determine column width first
-	width=0
-	for branch in $SHORT_NAMES; do
-		len=$(($(echo "$branch" | wc -c) - 1))
+	typeset -i width=0
+	typeset branch
+	for branch in $short_names; do
+		typeset -i len=$(($(echo "$branch" | wc -c) - 1))
 		width=$(max $width $len)
 	done
-	width=$(($width + 3))
+	width=width+3
 
-	for branch in $SHORT_NAMES; do
-		fullname="$PREFIX$branch"
-		base=$(git merge-base "$fullname" "$MASTER_BRANCH")
-		master_sha=$(git rev-parse "$MASTER_BRANCH")
-		branch_sha=$(git rev-parse "$fullname")
-		if [ "$fullname" = "$CURRENT_BRANCH" ]; then
+	typeset branch
+	for branch in $short_names; do
+		typeset fullname="$PREFIX$branch"
+		typeset base=$(git merge-base "$fullname" "$MASTER_BRANCH")
+		typeset master_sha=$(git rev-parse "$MASTER_BRANCH")
+		typeset branch_sha=$(git rev-parse "$fullname")
+		if [ "$fullname" = "$current_branch" ]; then
 			printf "* "
 		else
 			printf "  "
@@ -63,7 +68,8 @@
 			if [ "$branch_sha" = "$master_sha" ]; then
 				printf "(no commits yet)"
 			else
-				tagname=$(git name-rev --tags --no-undefined --name-only $base)
+				typeset tagname=$(git name-rev --tags --no-undefined --name-only $base)
+				typeset nicename
 				if [ "$tagname" != "" ]; then
 					nicename="$tagname"
 				else
diff --git a/gitflow-common b/gitflow-common
new file mode 100644
index 0000000..bcc6dbd
--- /dev/null
+++ b/gitflow-common
@@ -0,0 +1,147 @@
+#
+# git-flow -- A collection of Git extensions to provide high-level
+# repository operations for Vincent Driessen's branching model.
+#
+# Original blog post presenting this model is found at:
+#    http://nvie.com/archives/323
+#
+# Feel free to contribute to this project at:
+#    http://github.com/nvie/gitflow
+#
+# Copyright (c) 2010 by Vincent Driessen
+# Copyright (c) 2010 by Benedikt Böhm
+#
+
+# shell output
+warn() { echo "$@" >&2; }
+die() { warn "$@"; exit 1; }
+
+# set logic
+has() {
+	typeset item=$1; shift
+	echo " $@ " | grep -q " $item "
+}
+
+# basic math
+min() { [ "$1" -le "$2" ] && echo "$1" || echo "$2"; }
+max() { [ "$1" -ge "$2" ] && echo "$1" || echo "$2"; }
+
+# basic string matching
+startswith() { [ "$1" != "${1#$2}" ]; }
+endswith() { [ "$1" != "${1#$2}" ]; }
+
+# convenience functions for checking shFlags flags
+flag() { typeset FLAG; eval FLAG='$FLAGS_'$1; [ $FLAG -eq $FLAGS_TRUE ]; }
+noflag() { typeset FLAG; eval FLAG='$FLAGS_'$1; [ $FLAG -ne $FLAGS_TRUE ]; }
+
+#
+# Git specific common functionality
+#
+
+# get all available branches
+LOCAL_BRANCHES=$(git branch | sed 's/^[* ] //')
+REMOTE_BRANCHES=$(git branch -r | sed 's/^[* ] //')
+ALL_BRANCHES="$LOCAL_BRANCHES $REMOTE_BRANCHES"
+
+gitflow_test_clean_working_tree() {
+	if ! git diff --no-ext-diff --ignore-submodules --quiet --exit-code; then
+		return 1
+	elif ! git diff-index --cached --quiet --ignore-submodules HEAD --; then
+		return 2
+	else
+		return 0
+	fi
+}
+
+gitflow_require_clean_working_tree() {
+	gitflow_test_clean_working_tree
+	typeset -i result=$?
+	if [ $result -eq 1 ]; then
+		die "fatal: Working tree contains unstaged changes. Aborting."
+	fi
+	if [ $result -eq 2 ]; then
+		die "fatal: Index contains uncommited changes. Aborting."
+	fi
+}
+
+gitflow_require_local_branch() {
+	if ! has $1 $LOCAL_BRANCHES; then
+		die "fatal: Local branch '$1' does not exist and is required."
+	fi
+}
+
+gitflow_require_remote_branch() {
+	if ! has $1 $REMOTE_BRANCHES; then
+		die "Remote branch '$1' does not exist and is required."
+	fi
+}
+
+gitflow_require_branch() {
+	if ! has $1 $ALL_BRANCHES; then
+		die "Branch '$1' does not exist and is required."
+	fi
+}
+
+gitflow_require_branch_absent() {
+	if has $1 $ALL_BRANCHES; then
+		die "Branch '$1' already exists. Pick another name."
+	fi
+}
+
+#
+# gitflow_test_branches_equal()
+#
+# Tests whether branches and their "origin" counterparts have diverged and need
+# merging first. It returns error codes to provide more detail, like so:
+#
+# 0    Branch heads point to the same commit
+# 1    First given branch needs fast-forwarding
+# 2    Second given branch needs fast-forwarding
+# 3    Branch needs a real merge
+#
+gitflow_test_branches_equal() {
+	typeset commit1=$(git rev-parse "$1")
+	typeset commit2=$(git rev-parse "$2")
+	if [ "$commit1" != "$commit2" ]; then
+		typeset base=$(git merge-base "$commit1" "$commit2")
+		if [ "$commit1" = "$base" ]; then
+			return 1
+		elif [ "$commit2" = "$base" ]; then
+			return 2
+		else
+			return 3
+		fi
+	else
+		return 0
+	fi
+}
+
+gitflow_require_branches_equal() {
+	gitflow_require_local_branch "$1"
+	gitflow_require_remote_branch "$2"
+	gitflow_test_branches_equal "$1" "$2"
+	typeset -i status=$?
+	if [ $status -gt 0 ]; then
+		warn "Branches '$1' and '$2' have diverged."
+		if [ $status -eq 1 ]; then
+			die "And branch '$1' may be fast-forwarded."
+		elif [ $status -eq 2 ]; then
+			# Warn here, since there is no harm in being ahead
+			warn "And local branch '$1' is ahead of '$2'."
+		else
+			die "Branches need merging first."
+		fi
+	fi
+}
+
+#
+# gitflow_is_branch_merged_into()
+#
+# Checks whether branch $1 is succesfully merged into $2
+#
+gitflow_is_branch_merged_into() {
+	typeset subject=$1
+	typeset base=$2
+	typeset all_merges=$(git branch --contains $subject | sed 's/^[* ] //')
+	has $base $all_merges
+}
diff --git a/shFlags.sh b/gitflow-shFlags
similarity index 100%
rename from shFlags.sh
rename to gitflow-shFlags