Trick question. What do you think the following prints? 
perl -w -e'; @a=(split / /,"1 2 3 4 5")[1,2,1]; print "{",(join ",",@a
+),"}\n";'

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If you answered "{2,3,2}, of course", you'd be right, but only if you're using 5.8.0 or better.

Under 5.6.1, that prints "{2,3,}".

It behaves as if the list resulting from the split is some strange heisenbergian construct, where looking at a value destroys it.

Using 1,2,3 as an index list works, but re-using any index returns undef for the 2nd time it appears.

It IS fixed in 5.8.0, but I thought I should warn any fellow monks who might still be in 5.6.1 of this oddity...

EDIT: The behaviour isn't limited to split, either. This has the same problem: 

perl -e'$x="1 2 3 4 5"; @a=($x=~/\d+/g)[1,2,1]; print "{",(join ",",@a
+),"}\n";'

[download]

--
Mike

In reply to Interesting (split) oddity with 5.6.1, fixed in 5.8.0 by RMGir

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