Environment variable substitution in sed
Your two examples look identical, which makes problems hard to diagnose. Potential problems:
You may need double quotes, as in
sed 's/xxx/'"$PWD"'/'$PWDmay contain a slash, in which case you need to find a character not contained in$PWDto use as a delimiter.
To nail both issues at once, perhaps
sed 's@xxx@'"$PWD"'@'
In addition to Norman Ramsey's answer, I'd like to add that you can double-quote the entire string (which may make the statement more readable and less error prone).
So if you want to search for 'foo' and replace it with the content of $BAR, you can enclose the sed command in double-quotes.
sed 's/foo/$BAR/g'sed "s/foo/$BAR/g"In the first, $BAR will not expand correctly while in the second $BAR will expand correctly.