Compress PDF custom Oh-My-ZSH function

compress_pdf.zsh

# Place in $ZSH/.oh-my-zsh/custom.
#
# The following ZSH function uses GhostScript's `gs` command to reduce the file size of a PDF file.
# The result of compressing `test.pdf` will be written to `test.compressed.pdf`.
# If `test.compressed.pdf` exists, it will only be overwritten after confirmation.
#
# Now, restart/open a new shell and compress PDFs with:
#
#     compress_pdf test.pdf
#     File exists: test.compressed.pdf, overwrite (Y/n)? 
#     Wrote test.compressed.pdf.
#
# Based on https://gist.github.com/ahmed-musallam/27de7d7c5ac68ecbd1ed65b6b48416f9.

compress_pdf() {
    f="${1}"
    if [[ ! "${f}" =~ ^.*\.pdf ]]; then
        echo "Usage: compress_pdf FILE.pdf"
        return
    fi
    f2="${f/.pdf/.compressed.pdf}"
    if [[ -f "${f2}" ]]; then
        read "yn?File exists: ${f2}, overwrite (Y/n)? "
        if [[ "$yn" =~ [Nn] ]]; then
            echo "Not overwritting ${f2}, done."
            return
        fi
    fi
    gs \
        -q -dNOPAUSE -dBATCH -dSAFER \
        -sDEVICE=pdfwrite \
        -dCompatibilityLevel=1.3 \
        -dPDFSETTINGS=/screen \
        -dEmbedAllFonts=true -dSubsetFonts=true \
        -dColorImageDownsampleType=/Bicubic \
        -dColorImageResolution=144 \
        -dGrayImageDownsampleType=/Bicubic \
        -dGrayImageResolution=144 \
        -dMonoImageDownsampleType=/Bicubic \
        -dMonoImageResolution=144 \
        -sOutputFile="${f2}" \
        "${f}"
    echo "Wrote ${f2}."
}