Linux – redirecting “tail –follow=name | grep” to a file

grep SESSNUM=4437 *

Grep normally returns thing in order. Are you sure you are getting the results from the correct log file? Does it work correctly if you specify the logfile you want instead of just *?

Correction! There should only be one file in the directory that contains the session number, but I don't necessarily know which one when I'm grepping.

I would suggest you use the -H option of grep, so you can be sure you are getting the content from only one file. This should be the default behavior, but what you posted didn't include the filenames, unless you stripped those out.

   -H, --with-filename
          Print the file name for each match.  This is  the  default  when
          there is more than one file to search.

Something like this?

mkfifo child.fifo
tail -f child.out > child.fifo &
pid=$!
grep -q B child.fifo && kill $pid

in full:

#!/bin/sh    
rm -f child.out
./child.sh > child.out &
mkfifo child.fifo
tail -f child.out > child.fifo &
pid=$!
grep -q B child.fifo && kill $pid
rm child.fifo

Seems to run in 20 seconds.

$ time ./test2.sh

real    0m20.156s
user    0m0.033s
sys     0m0.058s

UPDATE

This way seems to work too:

#!/bin/sh
rm -f child.out
./child.sh > child.out &
(tail -f child.out | grep -q B child.out)

And if you're seeing it exit immediately sometimes, try adding a sleep 1, i.e.

#!/bin/sh
rm -f child.out
./child.sh > child.out &
sleep 1
(tail -f child.out | grep -q B child.out)