EXPR is interpolated and then executed as a system command. The collected standard output of the command is ret
urned. In scalar context, it comes back as a single (potentially multi-line) string. In list context, returns a list of lines (howev
er you've defined lines with $/ or
$INPUT_RECORD_SEPARATOR). This is the internal function implementing the
operator, but you can use it directly. The
operator is discussed in more detail in I/O Operators.