Short way to escape HTML in Bash?

Question

The box has no Ruby/Python/Perl etc.

Only bash, sed, and awk.

A way is to replace chars by map, but it becomes tedious

Answer 1

The previous sed replacement defaces valid output like

<

into

<

Adding a negative loook-ahead so "&" is only changed into "&" if that "&" isn't already followed by "amp;" fixes that:

sed 's/&(?!amp;)/\&/g; s//\>/g; s/"/\"/g; s/'"'"'/\'/g'