sed mystery

This morning, I was asked to provide a one-line startup command for a Docker container that should replace the second line of a specific file. While everyone seemed to agree that sed -i 's/oldword/newword/' file1.txt command should work, I discovered that it didn’t, at least not on the current version of macOS (13.3.1 Ventura).

After some research on Stack Overflow, I found that using sed -i '' 's/oldword/newword/' file1.txt might be the solution. However, back in 2014, sed -i"any_symbol" 's/oldword/newword/' file1.txt was the recommended approach.

Why did it change? I don’t know. Just sharing my experience in case someone stumbled upon the same issue.