re.pl: Variable not properly scoped inside block

Example:

~ $ re.pl
$ { my $abc = 10 ; $abc }
10
$ $abc
10
$ 

Is this a documented gotch开发者_如何学运维a?

This appears to be a bug in Lexical::Persistence, which Devel::REPL uses to manage the lexical environment persisting across multiple evals.

Here's a demonstration of the bug without Devel::REPL. This code incorrectly produces the value of $abc, 10, even though it's in an inner scope.

use strict;
use warnings;
use Lexical::Persistence;

my $environment = Lexical::Persistence->new;
$environment->call(sub {
    my $foo = shift;
    { my $abc = 10 };
    return $foo;
});

print $environment->get_context('_')->{'$abc'};

I've reported a bug against the module, we'll see what happens!

It's also worth noting that Matt Trout (the primary author of Devel::REPL)'s new lexical persistence module, Eval::WithLexicals does not suffer from this problem:

use strict;
use warnings;
use Eval::WithLexicals;

my $environment = Eval::WithLexicals->new;
print $environment->eval('{ my $abc = 10 ; $abc }'), "\n";
print $environment->eval('$abc'), "\n";

produces 10 as expected, then the second eval throws the expected Global symbol "$abc" requires explicit package name error.

$a and $b are special variables used for sorting. see perldoc -f sort.

Don't use $a or $b.

From Perlvar (Perl predefined variables) documentation:

$a $b

Special package variables when using sort(), see sort. Because of this specialness $a and $b don't need to be declared (using use vars , or our()) even when using the strict 'vars' pragma. Don't lexicalize them with my $a or my $b if you want to be able to use them in the sort() comparison block or function.

It doesn't happen if you run your code directly in the Perl interpreter:

$ perl -we '{ my $abc = 10 ; print "($abc)\n"; }; print "($abc)\n";'
Name "main::abc" used only once: possible typo at -e line 1.
(10)
Use of uninitialized value $abc in concatenation (.) or string at -e line 1.
()

May be you have found a bug in Devel::REPL.