I'm trying to read a log file which is being written to by a simple daemon. I would like to filter my "live" output to certain - multiple - "types".
My types are: DEBUG|INFO|WARN|ERROR|FATAL
This is what I have so far, and it works for one case, but I cannot get it working for multiple cases though.
tail -f log.txt | grep INFO
I've tried a couple of things to try and say I want "WARN's & ERROR's", but nothing is really working for me. How would I correct this?
In addition to switching to egrep/grep -E to get the alternation operator of extended regular expressions, you can you can also use multiple -e arguments to regular grep or even fgrep/grep -F
In fact, if your searches are all static strings (like the original question), you can even ‘downgrade’ all the way to fgrep/grep -F which might give a speed boost (since it always does direct string comparisons without regexps).
fgrep -e DEBUG -e INFO -e WARN -e ERROR -e FATAL
Also POSIX allows patterns to be separated by newlines.
# bash-ish to put a newlines into the string
fgrep $'DEBUG\nINFO\nWARN\nERROR\nFATAL'
# Standard syntax, but easier to break while editing(?):
fgrep "$(for f in DEBUG INFO WARN ERROR FATAL; do echo "$f"; done)"
This also works (regular grep and escape the pipe character):
tail -f log.txt | grep 'WARN\|ERROR'
