How to compress PDF in ubuntu using gs (Ghostscript)?

create a file named as main.sh:-

#!/bin/sh

gs  -q -dNOPAUSE -dBATCH -dSAFER \
    -sDEVICE=pdfwrite \
    -dCompatibilityLevel=1.3 \
    -dPDFSETTINGS=/screen \
    -dEmbedAllFonts=true \
    -dSubsetFonts=true \
    -dColorImageDownsampleType=/Bicubic \
    -dColorImageResolution=72 \
    -dGrayImageDownsampleType=/Bicubic \
    -dGrayImageResolution=72 \
    -dMonoImageDownsampleType=/Bicubic \
    -dMonoImageResolution=72 \
    -sOutputFile=out.pdf \
     $1

Then, run the script as following:- 

bash main.sh input.pdf