Reduce PDF File Size to still readable and printable State

pdf-compress.sh

#!/bin/bash
#
# Copyright 2021-2023 Martin Goellnitz
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#

function usage {
  echo "Usage: $0 [-m] file1 [file2...]" 1>&2
  echo "" 1>&2
  echo "  -m         modify file time of target file by a few seconds to keep mega syncing working" 1>&2
  exit 1
}

while getopts "m" opt ; do
  case "${opt}" in
    m)
      MEGA=true
      ;;
    *)
      usage
      ;;
  esac
done
shift $((OPTIND-1))

if [ -z "$*" ] ; then
  echo "Input filenames missing as parameters"
  echo ""
  usage
  exit 1
fi

while [ ! -z "$*" ] ; do
  INFILE="$1"
  shift
  if [ -f "$INFILE" ] ; then
    BASE=$(dirname "$INFILE")/$(basename "$INFILE" .pdf)
    ORIGINAL="${BASE}-orig.pdf"
    if [ -z "$(uname -v|grep Darwin)" ] ; then
      FILETIME=$(stat -c %Y -- "$INFILE")
    else
      FILETIME=$(stat -t %s -f %m -- "$INFILE")
    fi
    if [ ! -z "$MEGA" ] ; then
      FILETIME=$[ 4 +  $FILETIME ]
    fi
    # date -d '@'"$FILETIME"
    mv "$INFILE" "$ORIGINAL"
    # -dPDFSETTINGS=/screen
    # -dPDFSETTINGS=/prepress
    gs -sDEVICE=pdfwrite -dPrinted=false -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile="$INFILE" "$ORIGINAL"
    touch --date="$(date -R --date='@'$FILETIME)" "$INFILE"
    ORIGSIZE=$(stat -c %s -- "$ORIGINAL")
    # NEWSIZE=$(stat -c %s -- "$INFILE")
    NEWSIZE=$[ $(stat -c %s -- "$INFILE") + 2048 ]
    # echo $INFILE: $ORIGSIZE $NEWSIZE
    if [ "$ORIGSIZE" -le "$NEWSIZE" ] ; then
      # echo "Compressed file $INFILE would not be smaller"
      mv "$ORIGINAL" "$INFILE"
    else
     echo "$INFILE yields smaller file."
    fi
  else
    echo "$INFILE is not a file. Ignoring."
  fi
done