I don’t have any answers, but perhaps the following will shed some light?

12:08 >perl -v

This is perl 5, version 14, subversion 2 (v5.14.2) built for MSWin32-x
+86-multi-thread

...

12:08 >perl 318_SoPW.pl
1
 2

Use of uninitialized value in print at 318_SoPW.pl line 27.
Use of uninitialized value in print at 318_SoPW.pl line 27.

1
 2
 3

Use of uninitialized value in print at 318_SoPW.pl line 27.
Use of uninitialized value in print at 318_SoPW.pl line 27.
Use of uninitialized value in print at 318_SoPW.pl line 27.

1
 2
 3

1
2
3


12:08 >

[download]

but

12:11 >perl -v

This is perl 5, version 16, subversion 0 (v5.16.0) built for MSWin32-x
+86-multi-thread-64int
(with 1 registered patch, see perl -V for more detail)

...

12:11 >perl 318_SoPW.pl
1
 2

1
2

1
 2
 3

1
2
3

1
 2
 3

1
2
3


12:11 >

[download]

In neither case do I get a 4 in the output, as you do. Looks like there’s a Perl bug somewhere...

Update 1: Running on Vista 32-bit.

Update 2: With the local $_ line commented out, I get the following output (same for both perl versions):

17:59 >perl 318_SoPW.pl
Thread 1 terminated abnormally: Modification of a read-only value atte
+mpted at 318_SoPW.pl line 15.


Thread 2 terminated abnormally: Modification of a read-only value atte
+mpted at 318_SoPW.pl line 15.





18:00 >

[download]

Athanasius <°(((>< contra mundum

In reply to Re: One piece of code, two mysteries! by Athanasius
in thread One piece of code, two mysteries! (UPDATED.) by BrowserUk

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