A simple bash script to shrink PDFs based on ghostscript cli tool

shrinkpdf.sh

#!/bin/bash

## This program is free software: you can redistribute it and/or modify
## it under the terms of the GNU General Public License version 3 as published
## by the Free Software Foundation.
##
## 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 <https://www.gnu.org/licenses/>

# Check if system has ghostscript tool
if ! command -v gs &> /dev/null
then
	echo "ghostscript could not be found"
	echo "Please, install it and run this script again"
	exit 1
fi

# Check if at least one argument was passed
if [ -z "$1" ] || [ "$1" == "--help" ]
then
	echo -e "Use: $0 INPUT_PDF OUTPUT_PDF(OPTIONAL)\n"
	echo "In case an output file is omitted, the software will generate
	an output file appending ¨compressed¨ to the input file name"
	exit
fi

# check if the first argument is a PDF file
MIME=$(file -b --mime-type $1)

if [ "$MIME" != "application/pdf" ]
then
	echo "Input is not a valid PDF file"
	exit
fi

# Choose the quality output
CHOICE=0
VALID=false 

function pick_quality() {

	echo -e "\nWhat is your desired output?\n"
	echo " 1: screen: 72 dpi"
	echo " 2: ebook: 150 dpi"
	echo " 3: prepress: 300 dpi"
	echo -e "\nEnter number 1 to 3 below:"
	read CHOICE

	case $CHOICE in
		1) QUALITY="screen"
			VALID=true ;;
		2) QUALITY="ebook"
		   VALID=true;;
		3) QUALITY="prepress"
		   VALID=true;;
		*) echo -e "\e[31;1m \nYou typed an invalid number. Choose again: \e[m"
		   sleep 1 ;;
	esac
}

# Run pick_quality function until getting a valid input
while [ "$VALID" = false ]
do
	pick_quality
done

# Get the output file name
FILE_DIR=$(dirname $1)
FULL_FILE=$(basename $1)
FILE_NAME=${FULL_FILE%.*}
EXTENSION=${FULL_FILE##*.}
OUTPUT=""

if [ -n "$2" ]
then
	OUTPUT="$2"
else
	OUTPUT="${FILE_DIR}/${FILE_NAME}_compressed.${EXTENSION}"
fi

# Compressing the PDF
echo -e "\nCompressing..."
(gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/${QUALITY} -dNOPAUSE -dQUIET -dBATCH -sOutputFile=${OUTPUT} $1) &
wait
echo -e '\e[1A\e[KDone!'