Escape sed delimiter character when also regex special character -

say have want match string foo.. regex foo\., escape special meaning of . character.

now in sed command, use . delimiter.

for search like, say, cat, works fine.

echo cat | sed 's.cat.dog.g' 

but when have literal . in search string, run problem. think, since . delimiter, regex foo\. should become foo\\\.. ideally, first pass of unescaping done sed make foo\., , passed along regular expression engine.

but instead, matches cat\\\.

echo 'cat.' | sed 's.cat\\\..dog.g' # cat. echo 'cat\.' | sed 's.cat\\\..dog.g' # dog 

is there way make work literal . when . used delimiter?

i'm asking question because want able have function

function escapeforextendedsed ($str, $delimiter = "/") { ... } 

which can escape correctly depending on caller using delimiter.

this works me:

echo 'cat.' | sed 's.cat[\.].dog.g' # cat.