This is probably the simplest way...

my $String = "hello I went to the store yesterday and the day after an
+d the day after";

if ($String =~ m{yesterday .+? after})
{
    print $&;
}
[download]

perlvar warns though that use of $& can slow down your script considerably. If it's a small script and raw speed is not your prime concern, this is probably acceptable. If performance does become a concern though, the following should also do the trick and is almost as readable...

my $String = "hello I went to the store yesterday and the day after an
+d the day after";

if ($String =~ m{(yesterday .+? after)})
{
    print $1;
}
[download]