Note: There is a revised version of this script available.

While working on the typo3scripts project, I wanted to implement a self-updating feature into each of the scripts as that seemed most convenient for where these scripts would be used. My initial approach was OK but left me wondering.

So, here is the revised approach for a bash script that has the ability to update itself:

#!/bin/bash

set -o nounset
set -o errexit

SELF=$(basename $0)

# The base location from where to retrieve new versions of this script
UPDATE_BASE=http://typo3scripts.googlecode.com/svn/trunk

# Self-update
runSelfUpdate() {
  echo "Performing self-update..."
  
  # Download new version
  echo -n "Downloading latest version..."
  if ! wget --quiet --output-document="$0.tmp" $UPDATE_BASE/$SELF ; then
    echo "Failed: Error while trying to wget new version!"
    echo "File requested: $UPDATE_BASE/$SELF"
    exit 1
  fi
  echo "Done."
  
  # Copy over modes from old version
  OCTAL_MODE=$(stat -c '%a' $SELF)
  if ! chmod $OCTAL_MODE "$0.tmp" ; then
    echo "Failed: Error while trying to set mode on $0.tmp."
    exit 1
  fi
  
  # Spawn update script
  cat > updateScript.sh << EOF
#!/bin/bash
# Overwrite old file with new
if mv "$0.tmp" "$0"; then
  echo "Done. Update complete."
  rm \$0
else
  echo "Failed!"
fi
EOF
  
  echo -n "Inserting update process..."
  exec /bin/bash updateScript.sh
}

# Update check
SUM_LATEST=$(curl $UPDATE_BASE/versions 2>&1 | grep $SELF | awk '{print $1}')
SUM_SELF=$(md5sum $0 | awk '{print $1}')
if [[ "$SUM_LATEST" != "$SUM_SELF" ]]; then
  echo "NOTE: New version available!"
fi

It also includes the update check which wasn’t discussed over at StackOverflow. In case I revise the approach yet again, you’ll find the latest version over at the typo3scripts project page.