Hello there, I am not sure this is actually a bug as there may be reasons why it has to be this way, but certainly these tools work counter to my expectations.
I am trying to read lines from a log file and pass them through grep or sed, and then on to another tool (netcat, for example). What I am seeing is that: A) # tail trace.txt | grep "com" - WORKS: produces output B) # tail trace.txt | grep "com" | cat - WORKS: produces output C) # tail -f trace.txt | grep "com" - WORKS: produces output, then waits and reports new lines D) # tail -f trace.txt | grep "com" | cat - FAILS: no output from existing lines, never gets new data Similarly: A) # tail trace.txt | sed s/com/newcom/ - WORKS: produces output B) # tail trace.txt | sed s/com/newcom/ | cat - WORKS: produces output C) # tail -f trace.txt | sed s/com/newcom/ - WORKS: produces output, then waits and reports new lines D) # tail -f trace.txt | sed s/com/newcom/ | cat - FAILS: no output even from existing lines, no new data reported To me, it seems completely counterintuitive that A, B, and C would work, but D does not. Each line of input read by tail should be passed to STDOUT, which is then read as STDIN by grep/sed, then passed to STDOUT and read by cat. It should not matter if tail is "done" reading the output or not, as clearly that works fine in case C. Thoughts? Is there some limitation of which I am not aware that prevents this from working? Where does the data go in case D? Details: Linux moolap 2.6.16.60-0.30-smp #1 SMP Thu Aug 28 09:26:55 UTC 2008 x86_64 x86_64 x86_64 GNU/Linux tail (GNU coreutils) 5.93 GNU sed version 4.1.4 grep (GNU grep) 2.5.1 _______________________________________________ Bug-coreutils mailing list Bug-coreutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-coreutils
