Perl5 リファレンス

       readpipe EXPR
               EXPR is executed as a system command.  The
               collected standard output of the command is
               returned.  In scalar context, it comes back as a
               single (potentially multi-line) string.  In list
               context, returns a list of lines (however you've
               defined lines with `$/' or
               `$INPUT_RECORD_SEPARATOR').  This is the internal
               function implementing the `qx/EXPR/' operator, but
               you can use it directly.  The `qx/EXPR/' operator
               is discussed in more detail in the I/O Operators
               entry in the perlop manpage.