sub abc()
{
  $_ = 'x';
}

sub xyz()
{
  foreach(4..5)
  {
    print "  Before:$_\n";
    print "  After:$_\n";
  }
}

foreach(1..2)
{
  print "Before:$_\n";
  xyz();
  print "Mid:$_\n";
  abc();
  print "After:$_\n";
}
[download]

The above code produces

Before:1
  Before:4
  After:4
  Before:5
  After:5
Mid:1
After:x
Before:2
  Before:4
  After:4
  Before:5
  After:5
Mid:2
After:x
[download]

I have a simple loop which contains a call that assigns a value to $_. The sub actually does this with

This would indicate that $_ should be viewed as a global variable as used in abc(). However, in the xyz() sub $_ appears to be non-global as it leaves the $_ in the caller alone. What is the scope of $_ supposed to be?