With regular expressions, you can perform much more complex searches than the examples we've looked at so far by taking advantage of metacharacters. One of these metacharacters is the . (a period), which matches any single character:

$ grep dev.hda /etc/fstab
/dev/hda3       /               reiserfs        noatime,ro 1 1
/dev/hda1       /boot           reiserfs        noauto,noatime,notail 1 2
/dev/hda2       swap            swap            sw 0 0
#/dev/hda4      /mnt/extra      reiserfs        noatime,rw 1 1

In this example, the literal text dev.hda didn't appear on any of the lines in /etc/fstab. However, grep wasn't scanning them for the literal dev.hda string, but for the dev.hda pattern. Remember that the . will match any single character. As you can see, the . metacharacter is functionally equivalent to how the ? metacharacter works in glob expansions.