Grep is a powerful tool. It can do many things well. It can also be used in conjunction with other tools. If you are new to grep, it is a supercharged search tool. The basic format of the command is:
grep [options] PATTERN [FILE…]
Many options are available and described in the man page, so I won’t go into them here. I will just list some of my favorite grep commands. (who am I kidding? I just want a place to copy them from when I am not at my own computer)
#This command searches for a string and includes the preceding 5 lines and the 5 lines that follow it and shows the line numbers as well.
grep -n -B5 -A5 searchstring /tmp/filename
#This command uses grep to traverse the output from a find command.
find . -exec grep searchstring {} \; -print
#This command allows you to output a sorted list of connections from the month of Mar 2013
grep Mar/2013 /var/log/apache2/access.log | awk ‘{ print $1 }’ | sort -n | uniq -c | sort -rn | head
#Finding warnings and errors in your log
egrep -w ‘warning|error|critical’ /var/log/messages
