Is it possible to print the file size of a file?

\documentclass{book}


\begin{document}
\pdffilesize {example-image-duck.pdf}


\end{document}

pdftex has primitive for querying the file system:

\documentclass{article}
\usepackage{xfp}

\ExplSyntaxOn
\NewDocumentCommand{\filesize}{O{B}m}
 {
  \fpeval{ round( \pdffilesize { #2 } / \fp_use:c { c_brian_#1_fp } , 2) }
  \,#1
 }

\fp_const:Nn \c_brian_B_fp { 1 }
\fp_const:Nn \c_brian_KiB_fp { 1024 }
\fp_const:Nn \c_brian_MiB_fp { 1024*1024 }
\fp_const:Nn \c_brian_GiB_fp { 1024*1024*1024 }
\ExplSyntaxOff

\begin{document}

\filesize{../duck.jpg}

\filesize[KiB]{../duck.jpg}

\end{document}