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# 4.3. SDG Format

## Purpose

SDG files are used to format information extracted from source code by sdfget.

## Description

An SDG is a table of Key-Format pairs. For example:

         Key     Format
         -       "Key\t\tDescription\n"
         *       sprintf("%-15.15s\t%s\n", $key, $data)

The first line specifies the layout of the table and is required. An item is only printed if it has a description. The Key field can be one of the following:

- an item name
- a minus (-) character, indicating free text
- an asterix (*) character, indicating all remaining items

The Format field is a Perl expression. $key and $data are used to indicate the key and description of the current item respectively. Other available symbols are:

- $dir - directory component of current file
- $base - base component of current file
- $ext - extension component of current file
- $short - base & extension components of current file

## Examples

The SDG file used to format topics within the SDF documentation is:

    Key             Format
    -               "!use 'sdgmacs'\n!SDG_BEGIN\n"
    Title           "H1[id=\"$short\"] $short - $data\n\n"
    Purpose         "H2: $key\n\n$data\n\n"
    Interface       "H2: $key\n\n$data\n\n"
    -               "!SDG_DESCRIPTION_PRE\n"
    Description     "H2: $key\n\n$data\n\n"
    -               "!SDG_DESCRIPTION_POST\n"
    Notes           "H2: $key\n\n$data\n\n"
    Examples        "H2: $key\n\n$data\n\n"
    Limitations     "H2: Limitations and future directions\n\n$data\n\n"
    See_also        "H2: See also\n\n$data\n\n"
    Authors         "H2: $key\n\n$data\n\n"
    -               "!SDG_END\n"