Awk really has been superseded by Perl (and therefore arguably by Python, Ruby, etc.) But sed remains a thing of beauty, all its own, and very well worth learning. Hardly a day goes by that I don't use it in some one-off command like

    for i in *.png; do pngtopnm < $i | cjpeg > `echo $i | sed 's/png$/jpeg/'`; done