Shell scripting ,a bit of help please

[kektex]

Hi,
I`ve got a text file and what I want to do is add a certain text string to the end of each line.
Say for example my text file looks like this:
Hello line1
Hello line2
Hello line3
...

And I want to add the string "Bye" to the end of each line:
Hello line1 Bye
Hello line2 Bye
Hello line3 Bye
...

I am pretty sure there has to be a way of doing this with a bash script but I`ve trying to find out how and I cannot get it.Can someone give me a hand?

[kektex]

Just did it using vim (vi improved,a text editor):
:g/$/s// bye