phpman > perldoc > oct(644)

    oct EXPR
    oct     Interprets EXPR as an octal string and returns the corresponding
            value. An octal string consists of octal digits and, as of Perl
            5.33.5, an optional "0o" or "o" prefix. Each octal digit may be
            preceded by a single underscore, which will be ignored. (If EXPR
            happens to start off with "0x" or "x", interprets it as a hex
            string. If EXPR starts off with "0b" or "b", it is interpreted
            as a binary string. Leading whitespace is ignored in all three
            cases.) The following will handle decimal, binary, octal, and
            hex in standard Perl notation:

                $val = oct($val) if $val =~ /^0/;

            If EXPR is omitted, uses $_. To go the other way (produce a
            number in octal), use "sprintf" or "printf":

                my $dec_perms = (stat("filename"))[2] & 07777;
                my $oct_perm_str = sprintf "%o", $perms;

            The "oct" function is commonly used when a string such as 644
            needs to be converted into a file mode, for example. Although
            Perl automatically converts strings into numbers as needed, this
            automatic conversion assumes base 10.

            Leading white space is ignored without warning, as too are any
            trailing non-digits, such as a decimal point ("oct" only handles
            non-negative integers, not negative integers or floating point).