SED command in UNIX -

i want remove below string file in unix:

<?xml version='1.0' encoding='utf-8'?> 

the file content this:

<?xml version='1.0' encoding='utf-8'?>hello world 

in 1 single continuous line.

i using following command achieve same:

sed s'/<?xml version='1.0' encoding='utf-8'?>//g' myfile > myfile1 

however, resultant file myfile1 still having string.

how achieve ?

use double quotes outer quotes avoid escape issue:

sed "s/<?xml version='1.0' encoding='utf-8'?>//g" myfile > myfile1