Dynamic paper length

Last-Updated: 2023-05-17

Sources

• 2022-12/msg00100
  
• wimstockman/receipt_demo
  

Goal of the program

The Receipt Maker program (wimstockman/receipt_demo) was written by Wim Stockman to print receipts typeset with groff. However he was met with an issue: not knowing the paper length needed to print a receipt before typesetting it, while also needing to give this information to groff to typeset said receipt.

Solution implemented by Wim Stockman

His solution uses three steps:

• typesetting the receipt with groff a first time with an excessive paper length (here 66.5 cm);
• using this output to get the vertical position of the actual bottom of the receipt; and then
• typesetting the receipt for a second time with the real paper length.

This is achieved by outputting the vertical position reached at the end of the receipt to standard error with the following code (in the file receipt.tmac):

.tm \\n[nl]

This information is collected on the first pass (by only printing error messages with groff -z) and fed to groff on the second pass (in the file printreceipt.sh).