try

my $string="testing.123";
my @Strings;
@Strings=split(/\./,$string);
if($Strings[$#Strings] eq "123"){ DoSomething.... }

this way you have got the last chunk of the string divided by a period, always, because if there is more than one period then you might not get what you want, but if you have ONLY ONE period and can garrantee it, then use

my $string="testing.123";
my $string2;
($string,$string2)=split(/\./,$string);
if($string2 eq "123"){ DoSomething.... }

good luck!

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