Grep tips

search multiple patterns at once

You can grep for multiple patterns simultaneously without using extended regex sytax (--extended-regexp). Instead you can use multiple -e options. Each -e specifies a separate expression to match and `grep` will match each expression individually -- like an "or" subpattern.

For example the following greps for "ssh" in a `ps` listing, but also includes the column header which would otherwise be lost if you only grepped for "ssh":

# ps axwwo pid,ppid,etime,euser,cmd | grep -i -e ^\\s*PID -e ssh
  PID  PPID     ELAPSED EUSER    CMD
 5167     1  5-21:11:30 root     /usr/sbin/sshd
 6339  6291  5-21:11:06 noah     /usr/bin/ssh-agent x-session-manager
18562     1  4-01:16:17 noah     xterm -e ssh noah@web10
18563 18562  4-01:16:17 noah     ssh noah@web10

This is equivalent to:

# ps axwwo pid,ppid,etime,euser,cmd | grep -i --extended-regexp ^\\s*PID\|ssh

The first form using multiple -e options makes it easier to add on extra patterns without having to append it to an existing extended regex pattern. This makes it easy to make a nice 'psg' alias (ps grep):

alias psg='ps axwwo pid,ppid,pcpu,pmem,stat,etime,euser,cmd | grep -i -e ^\\s*PID -e '