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Re: The Lone Right Bracket

by turnstep (Parson)
on Jul 26, 2000 at 09:13 UTC ( [id://24414]=note: print w/replies, xml ) Need Help??

in reply to The Lone Right Bracket

Here's a simplified test case. For added fun, it also works with @, $ and *:
#!perl s//%/e; }

Eval is actually trying to use the surrounding code to try and finish it's evaluation. This was fixed. Recent version of perl (e.g. 5.6) will give this warning when the code above is run:

Bad evalled substitution pattern at line X

Looking at perl5004delta, we read that:

Perl (version 5) used to determine the value of EXPR inconsistently, sometimes incorrectly using the surrounding context for the determination. Now, the value of EXPR (before being parsed by eval) is always determined in a scalar context.

Unfortunately, each version keeps removing some of these little "features" that make for great obfuscated code. :)

Here's some fun code to try out if you have an "older" version of perl (older is in quotes because it hasn't been fixed *that* recently):

#!perl $foo = "ABC"; print "($foo)\n"; $foo =~ s/B/*/e; } print "($foo)\n";

Running this script produces this rather odd output:

(ABC) (A*main::} C)

In other words, eval tried so hard to evaluate something, it regarded the * as a typeglob, and created something unusual, to say the least. :)

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RE: Re: The Lone Right Bracket
by Miker (Scribe) on Jul 26, 2000 at 09:40 UTC
    Thanks for the insight, all the responses give me a lot to look into. To be honest the way I came across the oddity was late night typing but it seems that Perl mistakes are even beter learning experiences than everyday ones:)

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