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in reply to Mysterious append failure.

Lexical $b is out of scope. see 

 
D:\temp>perl -MO=Deparse -e "my $b = 1 for 1 .. 10"
;
foreach $_ (1 .. 10) {
    my $b = 1;
}
-e syntax OK

D:\temp>

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So, your code is the same as 

P:\test>perl -wl
my $a = 'a' x 10;
foreach $_ (0 .. 9)
    my $b .= substr( $a, $_, 10-$_ ) . '-' x $_;
}
print $main::b;
^Z
Use of uninitialized value in print at - line 3.

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Re^2: Mysterious append failure.
by gothic_mallard (Pilgrim) on Dec 09, 2004 at 12:35 UTC

    Ahh.. that looks like it makes sense. Was forgetting for a minute that declaring $b there would actually scope it inside the loop.

    D'oh.

    --- Jay

    All code is untested unless otherwise stated.
    All opinions expressed are my own and are intended as guidance, not gospel; please treat what I say as such and as Abigail said Think for yourself.
    If in doubt ask.

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[d/l]
      Was forgetting for a minute that declaring $b there would actually scope it inside the loop.
      This isn't quite true - the output of Deparse is wrong. The lexical is scoped wider than the loop, as can be seen here: 
      $ perl585 -le '$x=99; my $x = $_ for 1..3; print $x'

$

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      (Note that $::x isn't printed, the lexical $x is instead.) However, the initialising and releasing of $x is scoped to within the loop.

      That may be construed as a bug. There again, statement modifiers on my declarations are usally buggy, and are best avoided.

      Dave.

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[d/l]

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