Perl5 リファレンス

       formline PICTURE,LIST
               This is an internal function used by `format's,
               though you may call it, too.  It formats (see the
               perlform manpage) a list of values according to
               the contents of PICTURE, placing the output into
               the format output accumulator, `$^A' (or
               `$ACCUMULATOR' in English).  Eventually, when a
               `write' is done, the contents of `$^A' are written
               to some filehandle, but you could also read `$^A'
               yourself and then set `$^A' back to `""'.  Note
               that a format typically does one `formline' per
               line of form, but the `formline' function itself
               doesn't care how many newlines are embedded in the
               PICTURE.  This means that the `~' and `~~' tokens
               will treat the entire PICTURE as a single line.
               You may therefore need to use multiple formlines
               to implement a single record format, just like the
               format compiler.

               Be careful if you put double quotes around the
               picture, because an `@' character may be taken to
               mean the beginning of an array name.  `formline'
               always returns true.  See the perlform manpage for
               other examples.