merge lines of a txt file using shell script

merge lines of a txt file using shell script

I invoke a program from shell script and it creates an output file with
this format:
aaaaa\
bbbbb\
ccccc\
I would like to change this to:
aaaaabbbbbccccc
In VI editor I can just do ggVGJ and then replace all \ with "". But I
want to get this done via a script.