Q:

Is it possible to replace  with sed command?

I have been trying to replace  with  using this command       sed 's/</sys:String>/ /' but it doesnt work.

A:

either escape / with \
sed 's/<\/sys:String>/ /'

or use another separator (here comma : , )
sed 's,</sys:String>, ,'

A:

You can escape / with \:
sed 's/<\/sys:String>/ /'

Alternative to this is to use another separator. I like | instead of /. It looks good:
sed 's|</sys:String>| |'

