escaping quotes in bash variables

I often need to escape quotation characters or other special characters that are being piped into a bash process:

Say you have a mysql table which contains protein names. Some of these have the ' character in them (e.g. "Inosine 5' monophosphate dehydrogenase") and you want to do some bulk processing on these names, you could do something like this:

> mysql -u paulbo -N <<< "SELECT name from proteins" | while read protein_name; do mysql -u paulbo -N "SELECT count(*) FROM data INNER JOIN proteins ON data.protein_id = proteins.protein_id where proteins.name = '${protein_name//\'/\\\'}'"; done

Ah, three backslashes. Why didn't I think of that?

And sometimes you just want to output the text with the special characters all converted into something a bit more amenable (like the old and trusted '_').

> mysql -u paulbo -N <<< "SELECT name from proteins" | while read protein_name; do echo ${protein_name//[-\/\:\'\"\(\) ]/_};done