regex - replace a unknown string between two known strings with sed

Question

I have a file with the following contents:

WORD1 WORD2 WORD3

How can I use sed to replace the string between WORD1 and WORD3 with foo, such that the contents of the file are changed to the following?:

WORD1 foo WORD3

I tried the following, but obviously I'm missing something because that does not produce the desired results:

sed -i '' 's/WORD1.*WORD3/foo/g' file.txt

Answer 1

sed -i 's/WORD1.*WORD3/WORD1 foo WORD3/g' file.txt

or

sed -i 's/(WORD1).*(WORD3)/1 foo 2/g' file.txt

You might need to escape round brackets, depends on your sed variant.