# match positive and negative integers and reals 
use strict; 
my @numbers = my @strings = (); 
my @test_values = qw(abc 1 -2 3.3 -4.4 5. -6. .7 -.8); 
my $numcheck_pattern = qr/^\-?(?:\d+(?:\.\d+)?|\d+\.|\.\d+)\z/o; 
my $string = ''; 
foreach $string(@test_values) { 
    if ($string =~ /$numcheck_pattern/o) {  # Is this /o necessary or redundant? 
        push(@numbers, $string); 
    } else { 
        push(@strings, $string); 
    } 
} 
print 'strings: "' . join(', ', @strings) . qq|"\n|; 
print 'numbers: "' . join('" "', @numbers) . qq|"\n|; 
 
__END__ 
# output 
strings: "abc" 
numbers: "1" "-2" "3.3" "-4.4" "5." "-6." ".7" "-.8"

my $numcheck_pattern = qr/^    # absolute beginning of string 
                         \-    # negative sign 
                         ?     # quantify negative sign as optional 
                         (     # contain sub expression to dilineate alternatives 
                         ?:    # don't capture match into \1 or $1 
 
                               # first alternative matches eg "1" or "1.1" 
                               \d+  # one or more integer chars 
                               (    # contain sub expression for benefit of "?" quantifier 
                               ?:   # don't capture match into \2 or $2 
                                   \.     # decimal point 
                                   \d+    # one or more integer chars 
                               )    # end second sub expression containment 
                               ?    # quantify decimal portion as optional 
 
                            |  # second alternative matches eg "1." 
                               \d+  # one or more integer chars 
                               \.   # decimal point 
 
                            |  # third alternative matches eg ".1" 
                               \.  # decimal point 
                               \d+ # one or more integer chars 
 
                         )     # end first sub expression containment 
                         \z    # absolute end of string 
                         /xo;  # extended, only compile once