Continuous grep, output at same spot on console - linux

Question

I use
tail -f file | grep pattern
all the time for continuous grep.
However, is there a way I can make grep output its pattern at the same spot, say at the top of the screen? so that the screen doesn't scroll all the time?
My case is something like this: tail -f log_file | grep Status -A 2 will show the current status and what changed it to that status. The problem is the screen scrolls and it becomes annoying. I'd rather have the output stuck on the first 3 lines in the screen.
Thank you!

Answer 1

you could use the watch command; which will always execute the same command, but the position on the screen will stay the same. The process might eat some more CPU or memory though:
watch "tail file | grep pattern"
by default watch executes that command every 2 seconds. You can adjust up to 0.1 seconds using:
watch -n 0.1
NOTE
As noted by #etanReisner: this is not exactly the same as tail -f: tail -f will change immediately if something is added to your logfile, the watch command will only notice that when it executes, ie every 2 (or 0.1 seconds).

Answer 2

Assuming you are using a vt100 compatible emulator...
This command will tail a file, pipe it into grep, read it a line at a time and then display it in reverse on the top line of the screen:
TOSL=$(tput sc;tput cup 0 0;tput rev;tput el)
FROMSL=$(tput sgr0; tput rc)
tail -f file | grep --line-buffered pattern | while read line
do
echo -n "$TOSL${line}$FROMSL"
done
It assumes your output appears a line at a time. If you want more than one line, you can read more than a line, but you have to decide how you want to buffer the output. You could also use the csr terminfo command to set up an entire separate scrolling region instead of just having one line.
Here is the scrolling region version with a ten line status area at the top:
TOSL=$(tput sc; tput csr 0 10; tput cup 10 0;tput rev;tput el)
FROMSL=$(tput sgr0; tput rc;tput csr 10 50;tput rc)
tail -f file | grep --line-buffered pattern | while read line
do
echo -n "$TOSL${line}
$FROMSL"
done
Note that it is not impossible that your display will be corrupted from time-to-time as it could be that the output from your main shell and your background task get mixed up.

Answer 3

Simply replace the newlines with carriage returns.
tail -f file | grep --line-buffered whatever | tr '\012' '\015'
The line buffering is to avoid jumpy output; see http://mywiki.wooledge.org/BashFAQ/009
This is quick and dirty. As noted in comments, this will leave the previous contents of the line underneath, so a shorter line will not completely overlay a longer line. You could add some control codes to address that, but then you might as well use Curses for the formatting too, like in rghome's answer.