Quotes

Arguments are separated by spaces

If you want to include spaces in your arguments, enclose them in quotes:

      $ grep 'Reegen Hatch' /etc/passwd
      reegen:x:1000:1000:Reegen Hatch:/home/reegen:/bin/ksh

      $ grep "George's"  my.email.txt
      Everyone loves to ride in George's pontoon boat.

Double quotes allow variable and backtick expansion.
Single quotes don't.