Brew clean up script

brew_cleanup.sh

#!/bin/bash
#
# Clear out old, inactive versions of software
# installed by Homebrew.
# Created by Colin and listed on http://www.nonsenseby.me/blog/2014/01/12/remove-old-versions-in-homebrew/
#
set -o noglob
# Some brew settings.
readonly BREW_CMD=$( which brew )
readonly BREW_AWK="/tmp/brew.$$.awk"

# Create temporary awk script.
cat > $BREW_AWK <<EOF
BEGIN {sw=0; used="";}

\$0 ~ cellar { 
  n=split(\$1,r,"/");
  if (\$NF == "\*") { 
      used=r[n];
  } 
  else {
      vers[sw++] = r[n];
  }
} 

END {
  if (used != "" && sw>0) {
      for (idx in vers) {
          system(brew " switch " tap " " vers[idx]);
          system(brew " remove " tap);
      }
      system(brew " switch " tap " " used);
  }
}
EOF

# Get a list of installed things
readonly INSTALLED_FORMS=$( ${BREW_CMD} list )

for tap in $INSTALLED_FORMS
do
  # Cellar location for this tap
  # ex: /usr/local/Cellar/PROGRAM
  cellar=$( ${BREW_CMD} --cellar ${tap} )
  # Escape all the slashes: / -> \/
  awk_cellar=$( ${BREW_CMD} --cellar ${tap} | sed -e 's/\//\\\//g')
  # Pass the tap info to the AWK script.
  ${BREW_CMD} info ${tap} | awk -v brew="$BREW_CMD" -v cellar="$awk_cellar" -v tap="$tap" -f $BREW_AWK
done

# Clean-up temporary script.
rm $BREW_AWK