The $ is a sigil, so it appears before variables like $var, so it's just saying | it out. When typed at the beginning of a one liner it becomes quite obvious what you want. This is clearly not a feature for a large project, but a quick UNIX style one off awk-like script.
In Perl `$` is strictly a scalar variable though this can be a reference to an array, hash or object as they are stored as references. Not to be confused with `$` in PHP which simply denotes a variable of any kind. In Bash `$` denotes the value of a variable.
The $ is a sigil, so it appears before variables like $var, so it's just saying | it out. When typed at the beginning of a one liner it becomes quite obvious what you want. This is clearly not a feature for a large project, but a quick UNIX style one off awk-like script.