I am trying to capture output from an install script (that uses scp) and log it. However, I am not getting everything that scp is printing out, namely, the progress bar. <
It looks like your just missing whether the scp was succesful or not from the log.
I'm guessing the scroll bar doesn't print to stdout and uses ncurses or some other kind of TUI?
You could just look at the return value of scp to see whether it was successful. Like
scp myfile user@host.com:. && echo success!
man scp says
scp exits with 0 on success or >0 if an error occurred.