Programming Perl, 4th Edition

Footers

While $^ ($FORMAT_TOP_NAME) contains the name of the current header format, there is no corresponding mechanism to do the same thing automatically for a footer. Not knowing how big a format is going to be until you evaluate it is one of the major problems. It’s on the to-do list.^[232]

Here’s one strategy: if you have a fixed-size footer, you can get footers by checking $– ($FORMAT_LINES_LEFT) before each write, and then print the footer yourself if necessary.

Here’s another strategy: open a pipe to yourself using open(MESELF, "|–") (see the open entry in Chapter 27), and always write to MESELF instead of STDOUT. Have your child process postprocess its STDIN to rearrange headers and footers however you like. Not very convenient, but it’s doable.

^[232] That doesn’t guarantee we’ll ever do it, of course. Formats are somewhat passé in this age of WWW, Unicode, XML, XSLT, and whatever the next few things after that are.