LOL!

perl -e 'print+(split"-",(grep(/X-(?!Powered)/,`HEAD www.slashdot.org`))[0],2)[1]'

Added: This version works with AS Perl!
perl -e "print+(split'-',(grep(/X-(?!Powered)/, `HEAD www.slashdot.org`))[0],2)[1]"

Updated: made correction suggested by diotalevi