perldoc -f printf

    printf FILEHANDLE FORMAT, LIST
    printf FORMAT, LIST
            Equivalent to "print FILEHANDLE sprintf(FORMAT, LIST)", except
            that "$\" (the output record separator) is not appended. The
            first argument of the list will be interpreted as the "printf"
            format. If "use locale" is in effect, the character used for the
            decimal point in formatted real numbers is affected by the
            LC_NUMERIC locale. See the perllocale manpage.

            Don't fall into the trap of using a "printf" when a simple
            "print" would do. The "print" is more efficient and less error
            prone.


perldoc perllocale 

Category LC_NUMERIC: Numeric Formatting
In the scope of use locale, Perl obeys the LC_NUMERIC locale information, which controls an application's idea of how numbers should be formatted for human readability by the printf(), sprintf(), and write() functions. String-to-numeric conversion by the POSIX::strtod() function is also affected. In most implementations the only effect is to change the character used for the decimal point--perhaps from '.' to ','. These functions aren't aware of such niceties as thousands separation and so on. (See The localeconv function if you care about these things.)

Output produced by print() is also affected by the current locale: it depends on whether use locale or no locale is in effect, and corresponds to what you'd get from printf() in the ``C'' locale. The same is true for Perl's internal conversions between numeric and string formats:

        use POSIX qw(strtod);
        use locale;
        $n = 5/2;   # Assign numeric 2.5 to $n
        $a = " $n"; # Locale-dependent conversion to string
        print "half five is $n\n";       # Locale-dependent output
        printf "half five is %g\n", $n;  # Locale-dependent output
        print "DECIMAL POINT IS COMMA\n"
            if $n == (strtod("2,5"))[0]; # Locale-dependent conversion