Rather interesting behavior. If you merely use @_'s magic aliasing, the results seem even stranger.
#! perl -slw
use strict;
sub recurse {
print \$_[0];
print ">> '$_[ 0 ]'";
if( length $_[ 0 ] ) {
recurse( substr( $_[ 0 ] , 1, -1 ) );
$_[0] = " ( $_[0] ) ";
}
print "<< '$_[0]'";
return;
}
my $str = 'abcdefghij';
recurse $str;
print $str;
__END__
SCALAR(0x8126a70)
>> 'abcdefghij'
LVALUE(0x8126bc0)
>> 'bcdefghi'
SCALAR(0x812a454)
>> 'cdefgh'
SCALAR(0x812a520)
>> 'defg'
SCALAR(0x812a5ec)
>> 'ef'
SCALAR(0x812a6b8)
>> ''
<< ''
<< ' ('
<< ' ( d'
<< ' ( c ('
<< ' ( b ( c'
<< ' ( a ( b ( c ( ) d ) ( ) ef ) ghij ) '
( a ( b ( c ( ) d ) ( ) ef ) ghij )
Perhaps this is a bug in the magic lvalue-ness of substr? It doesn't seem to be verifying the length of an lvalue on an lvalue, thus the shifting of the terms that appear on the right.