DB<12> use strict;print  @$b
Can't use an undefined value as an ARRAY reference at (eval 39)[/data/
+data/com.termux/files/usr/lib/perl5/5.28.2/perl5db
+.pl:738] line 2.

  DB<13> use strict;print  @$b=(1..3)
123
  DB<14> p $b
ARRAY(0xb0a92180)
  DB<15>
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Using $a or $b triggers a special case for sort. This can be seen by using some other variable name instead:

>perl -w -Mstrict -E 'say @$b'
Can't use an undefined value as an ARRAY reference at -e line 1.
>perl -w -Mstrict -E 'say @$c'
Global symbol "$c" requires explicit package name (did you forget to d
+eclare "my $c"?) at -e line 1.
Execution of -e aborted due to compilation errors.
>perl -w -Mstrict -E 'say @$b=(1..3)'
123
>perl -w -Mstrict -E 'say @$c=(1..3)'
Global symbol "$c" requires explicit package name (did you forget to d
+eclare "my $c"?) at -e line 1.
Execution of -e aborted due to compilation errors.
>
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Alexander