C:\@Work\Perl>perl -wMstrict -e "sub S { if (! $_[0]) {} }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<>
<>

C:\@Work\Perl>perl -wMstrict -e "sub S { if (  $_[0]) {} }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<>
<>

C:\@Work\Perl>perl -wMstrict -e "sub S { unless (! $_[0]) {} }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<1>
<>

C:\@Work\Perl>perl -wMstrict -e "sub S { unless (  $_[0]) {} }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<>
<hiya>

C:\@Work\Perl>perl -wMstrict -e "sub S { do {} if ! $_[0] }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<>
<>

C:\@Work\Perl>perl -wMstrict -e "sub S { do {} if   $_[0] }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<>
<>

C:\@Work\Perl>perl -wMstrict -e "sub S { do {} unless ! $_[0] }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<1>
<>

C:\@Work\Perl>perl -wMstrict -e "sub S { do {} unless   $_[0] }
print qq(<@{[ S($_) ]}> \n) for @ARGV"   ""  "hiya"
<>
<hiya>