setenv sets enviorment variables in a unix system. I would assume it is in a file with a leading #!/bin/sh at the top. All it does is set these enviorment variables to the corrosponding filenames when it is run by the shell.

Your assumption is correct in that you can now access these vars from a perl script using %ENV
ie. $ENV{WP_DEFAULT_CONFIG_DIR}

On other systems you may have to set the enviorment vars with: export VAR=value

To format code use
<code> and </code>
The rest can be formatted with standard HTML.
HTH