preinst is in tgif 1:4.2.5-1.2.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31  | #!/bin/sh -e
case $1 in
   abort-upgrade ) 
   exit 0
   ;;
   install|upgrade )
   if [ ! -z "$2" ]; then
      # Remove old config file if upgrading from tgif <= 3.0p13-1
      rm -rf /etc/X11/tgif
      # Clean up app-defaults files from previous versions of the postinst
      # script tgif (< 4.2.2-4).  This should restore the files to their
      # pristine state unless the user has made additional alterations.
      for bit in "" "/ja_JP.eucJP" "/ru"; do
          file=/etc/X11$bit/app-defaults/Tgif
          # Remove all instances of the 
          #   Tgif*InitialPaperSize:
          #   Tgif*GridSystem:
          # line pairs appended by old versions of postinst.
          sed '/Tgif\*InitialPaperSize/,+1 d' $file > $file.clean
          mv $file.clean $file
      done
   fi
   ;;
   * )
   echo "preinst called with unknown argument \`$1'" >&2
   exit 1
   ;;
esac
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