How to use sed to change file extensions?

Question

I have to do a sed line (also using pipes in Linux) to change a file extension, so I can do some kind of mv *.1stextension *.2ndextension like mv *.txt *.

Answer 1

you can use string manipulation

filename="file.ext1"
mv "${filename}" "${filename/%ext1/ext2}"

Or if your system support, you can use rename.

Update

you can also do something like this

mv ${filename}{ext1,ext2}

which is called brace expansion