Pair of scripts for automatically updating the build number for Xcode projects. The second one restores the number so you have no outgoing version control changes.

restore_build_number.sh

#!/bin/sh
# Set in Product | Scheme | Edit Scheme | Build | Post-actions as a new Run Script item. 
#   echo Restoring build number
# 	${PROJECT_DIR}/Scripts/restore_build_number.sh
# Select your target in the "Provide build settings from" dropdown. 
set -e

if [ -z "$SRCROOT" ]
then
	echo "Run this from the project root."
	export SRCROOT=`pwd`
	echo "Setting SRCROOT to $SRCROOT"
fi

if [ -z "$INFOPLIST_FILE" ]
then
	export INFOPLIST_FILE=YOUR_PROJECT/YOUR_PROJECT-Info.plist
	echo "Setting INFOPLIST_FILE to $INFOPLIST_FILE"
fi

if [ -f "$SRCROOT/Scripts/previous_build_number.txt" ]
then
	CFBundleVersion=`cat $SRCROOT/Scripts/previous_build_number.txt`
else
	exit 0
fi
echo Restoring CFBundleVersion to $CFBundleVersion
[ -f "$SRCROOT/Scripts/previous_build_number.txt" ] && rm -f "$SRCROOT/Scripts/previous_build_number.txt"

/usr/libexec/PlistBuddy -c "Set :CFBundleVersion $CFBundleVersion" "$SRCROOT/$INFOPLIST_FILE"

udpate_build_number.sh

#!/bin/sh
# Set in Product | Scheme | Edit Scheme | Build | Pre-actions as a new Run Script item. 
#   echo Updating build number
# 	${PROJECT_DIR}/Scripts/update_build_number.sh
# Select your target in the "Provide build settings from" dropdown. 
# NOTE: You need to change YOUR_PROJECT with your actual project name. 
set -e

if [ -z "$SRCROOT" ]
then
	echo "Run this from the project root."
	export SRCROOT=`pwd`
	echo "Setting SRCROOT to $SRCROOT"
fi

if [ -z "$INFOPLIST_FILE" ]
then
	export INFOPLIST_FILE=YOUR_PROJECT/YOUR_PROJECT-Info.plist
	echo "Setting INFOPLIST_FILE to $INFOPLIST_FILE"
fi

# Clean slate, if needed, to start. 
# Sometimes Xcode is lame and doesn't complete the Post-action reset. 
$SRCROOT/Scripts/restore_build_number.sh

CFBundleVersion=$(/usr/libexec/PlistBuddy -c "Print CFBundleVersion" "$SRCROOT/$INFOPLIST_FILE")
echo CFBundleVersion was $CFBundleVersion

# Save for restoration; to avoid outgoing VCS change. 
[ -f "$SRCROOT/Scripts/previous_build_number.txt" ] && rm -f "$SRCROOT/Scripts/previous_build_number.txt"
echo $CFBundleVersion > $SRCROOT/Scripts/previous_build_number.txt

DotTimestamp=$(date '+.%m%d%H%M')
echo Appending timestamp of $DotTimestamp

CFBundleVersion=$CFBundleVersion$DotTimestamp
echo Updating CFBundleVersion to $CFBundleVersion

/usr/libexec/PlistBuddy -c "Set :CFBundleVersion $CFBundleVersion" "$SRCROOT/$INFOPLIST_FILE"