Sed command to edit a txt file doesn't work : I'm not a developer or anything close to IT, I'm a medical student,  I'm just trying to use tasker to edit an xml file using sed shell command. 
So I was testing on txt file and the command was the following:

"" sed -i 's+<boolean name="EnablePreviewAll" value="false"/>+<boolean name="EnablePreviewAll" value="true"/>+' /storage/emulated/0/basel.txt ""

It doesn't give me an error but the value doesn't change at all.
(I'm using Termux with root access)