<p>When using regular expressions in Ruby, what is the difference between $1 and \1?</p>

\1 is a backreference which will only work in the same
```
sub
```
or
```
gsub
```
method call, e.g.:
```
```
"foobar".sub(/foo(.*)/, '\1\1') # => "barbar"
```
```
$1 is a global variable which can be used in later code:
```
```
if "foobar" =~ /foo(.*)/ then 
  puts "The matching word was #{$1}"
end
```
```
Output:
```
```
"The matching word was bar"
# => nil
```
```