Easiest Filter Code

i am trying to code a program to load a file filter out randomtext & "/register" & Random text on a single line and re write the file

what is the easyest code to do this

Example

input
blahg blah
blah blah
blah blajh /register blasdf asdf <-- wanna get rid of this line only | filter
asdfasdf
asdfasdf
asdsdfasdf

Output
blahg blah
blah blah
asdfasdf
asdfasdf
asdsdfasdf