I'm not understanding the @{[]} syntax, although I do recognize the array index [], the hash {}, and the array @ -- can you explain what is going on, please?

The array index isn't an array index, the hash isn't a hash.
@{ } dereferences an array reference. ${ } dereferences a scalar reference. [ ] constructs an array refrence, \ constructs a scalar reference. So, instead of writing 

This program does this and that with the @{[OUT_DIR]}. The filename is
@{[OUT_FILENAME]} and the file suffix is @{[OUT_SUFXSTOR]}.

Fields are separated with the @{[OUT_FIELDSEP]} character. Enter a val
+ue
between @{[VAL_MIN]} and @{[VAL_MAX]}.

[download]

as in BrowserUk's example, you could also write 

This program does this and that with the ${\OUT_DIR}. The filename is
${\OUT_FILENAME} and the file suffix is ${\OUT_SUFXSTOR}.

Fields are separated with the ${\OUT_FIELDSEP} character. Enter a valu
+e
between ${\VAL_MIN} and ${\VAL_MAX}.

[download]

The reference implementation in perl is the author's way of introducing ásbestos gélōs into the language, great fun and a good opportunity to distinguish yourself with expertise, once you grok cause and syntax.

Quick, what does ~@~ mean?

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In reply to Re^3: How to interpolate CONSTANTS in Here docs? by shmem
in thread How to interpolate CONSTANTS in Here docs? by CoVAX

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