Searching a specific line in a large file

Hey All

Can any one please suggest the procedure to search a part of line in a very large file in which log entries are entered with very high speed.

i have trued with grep and egrep

grep 'text text text' <file-name>

egrep 'text text text' <file-name>

here 'text text text' is something which i have selected from file itself

tail -f thatlogfile | grep "text text text" > filteredlog
# or to see it on the screen and write it parallel into a file
tail -f thatlogfile | grep "text text text" | tee filteredlog

Thanks Zaxxon

Actually our requirement is to find a specific error line in a very lagre log file which is heavily appended with many log entries.
And on every occurenceof the error we have to sent a mail alert .

please suggest

Here is some idea to do this --
--------------------------------
ls -1 | while read record;do
rv=`echo $record | grep -w "ERROR-STRING"`
if [ $? -eq 0 ]
then
mailx -s "Error found in record - $record " xxxx@yourcompany.com
fi
done

Thanks all,

i have used
grep 'text to be searched' $myFile > test

as using tail -f $myFile | grep 'error'

im unable to set a exit condition.