You're completly right :-)

use Time::Local;

my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(t
+ime);

# Yesterday is one second before the beginning of today:
my $Yesterday = timelocal(0,0,0,$mday,$mon,$year) - 1;

my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($
+Yesterday);
++$mon;
$year += 1900;

print "Yesterday: $mday.$mon.$year\n";
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