Question: What does this expression in Perl programming do?

```
$variable =~ /^\s*$/;

```

Answer: 
That's looking for a line start (^), followed by zero or more whitespace (\s\*) characters, followed by a line end ($).

It's essentially looking for blank/empty lines. 

I'd expect the expression to be used in something like:

```
if ($v =~ /^\s*$/) {
   # found a blank line
}

```

in order to perform the check and a following action.
`=~` is a match operator.

The statement returns true if $variable only consists of spaces, or is simply empty.

So it just checks if the string is empty or not.