Programming Perl, 4th Edition

Numeric Literals

Numeric literals are specified in any of several customary^[47] floating-point or integer formats:

my $x = 12345;                # integer
my $x = 12345.67;             # floating point
my $x = 6.02e23;              # scientific notation
my $x = 4_294_967_296;        # underline for legibility
my $x = 0377;                 # octal
my $x = 0xffff;               # hexadecimal
my $x = 0b1100_0000;          # binary

Because Perl uses the comma as a list separator, you cannot use it to separate the thousands in a large number. Perl does allow you to use an underscore character instead. The underscore only works within literal numbers specified in your program, not for strings functioning as numbers or data read from somewhere else. Similarly, the leading 0x for hexadecimal, 0b for binary, and 0 for octal work only for literals. The automatic conversion of a string to a number does not recognize these prefixes—you must do an explicit conversion^[48] with the oct function—which works for hex and binary numbers, too, as it happens, provided you supply the 0x or 0b on the front.

^[47] Customary in Unix culture, that is. If you’re from a different culture, welcome to ours!

^[48] Sometimes people think Perl should convert all incoming data for them. But there are far too many decimal numbers with leading zeros in the world to make Perl do this automatically. For example, the zip code for the O’Reilly Media office in Cambridge, Massachusetts, is 02140. The postmaster would get confused if your mailing label program turned 02140 into 1120 decimal.