# Create GIF header + HTML inside a comment block
echo -e "GIF89a\x01\x00\x01\x00\x80\x00\x00\xff\xff\xff\x00\x00\x00!\xfe\x12" > polyglot.html.gif
echo -n "Hello
" >> polyglot.html.gif
# Append minimal GIF footer
echo -e "\x00;" >> polyglot.html.gif
# Now:
open polyglot.html.gif # Browser renders HTML
# OR
display polyglot.html.gif # Image viewer shows corrupted GIF (or ignores comment)