$& receives the part of the string that was matched by the pattern,
$` receives the part of the string that preceded the match
$' receivesthe string after the match.
def show_regexp(a, re)
if a =~ re
"#{$`}<<#{$&}>>#{$'}"
else
"no match"
end
end
puts show_regexp('very interesting', /t/)
puts show_regexp('this is a test', /a/)
puts show_regexp('these are all tests', /ll/)
puts show_regexp('zeller', /z/)