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Dying and Swearing

by Abigail (Deacon)
 on Jun 01, 2001 at 10:47 UTC Need Help??

```eval {die [[qq [Just another Perl Hacker]]]};; print
\${\${\${@}}[\$#{@{\${@}}}]}[\$#{\${@{\${@}}}[\$#{@{\${@}}}]}]

-- Abigail

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"Dying and Swearing" explained
by BooK (Curate) on Jun 01, 2001 at 17:09 UTC

Very good one! This is what I call unreadable...

You are using a propriety of die() I didn't know of...

die() can also be called with a reference argument. If this happens to be trapped within an eval(), \$@ contains the reference.

So after the eval() died \$@ contains a reference to an array holding only one element, which is a reference to an array containing the string "Just another Perl hacker". But what does the print() actually print?

Let's cut the all thing in several bits: first you must know that \$#{@{\${@}}} equals 0. Here is why: when you see \$#a, this is the value of the last array index (one less than the size of the array) of the array @a. @{\${@}} is an array dereference. Since \$@ is an array holding only one value, the result is 0.

We now have to understand \${\${\${@}}[0]}[\$#{\${@{\${@}}}[0]}]... We recognize the underlined part as an index value. Let's calculate it.

• \${\${@}}[0] is the first element of the array reference by \$@ (which is another reference to the array holding the string we want to print).
• In \$#{\${@{\${@}}}[0]} the underlined part is an array (dereferenced from \$@). The \$#<array> notation will give us the value of the last index of the array, which is 0.

With \${\${\${@}}[0]}[0], we are almost there. The underlined part is an array dereference, from which we want the first element.

This element is "Just another Perl hacker". QED.

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