纯笔记，内容来自《Learning Perl 5th Edition》

  • printf "Hello, %s; your password expires in %d days!\n", $user, $days_to_die;

  • To print a number in what’s generally a good way, use %g, which automatically chooses floating-point, integer, or even exponential notation as needed:
    printf "%g %g %g\n", 5/2, 51/17, 51 ** 17; # 2.5 3 1.0683e+29

“General” numeric conversion. Or maybe a “Good conversion for this number” or “Guess what I want the output to look like.”

  • The %d format means a decimal integer, truncated as needed:
    printf "in %d days!\n", 17.85;# in 17 days!

Note that this is truncated, not rounded. In Perl, printf is most often used for columnar data, since most formats accept a field width. If the data won’t fit, the field will generally be expanded as needed: printf “m\n”, 42; # output like ````42 (the ` symbol stands for a space) printf “-\n”, 2e3 + 1.95; # 2001

There’s also %x for hexadecimal and %o for octal if you need those. But we really say “decimal” here as a memory aid: %d for decimal integer.

  • The %s conversion means a string, so it effectively interpolates the given value as a string, but with a given field width:
printf "s\n", "wilma";# looks like `````wilma

A negative field width is left-justified (in any of these conversions):

printf "%-15s\n", "flintstone"; # looks like flintstone`````
  • The %f conversion (floating-point) rounds off its output as needed, and even lets you request a certain number of digits after the decimal point:
    printf "f\n", 6 * 7 + 2/3;
    printf ".3f\n", 6 * 7 + 2/3;
    printf ".0f\n", 6 * 7 + 2/3;
    # looks like ```42.666667
    # looks like ``````42.667
    # looks like ``````````43

  • To print a real percent sign, use %%, which is special in that it uses no element from the list: printf "Monthly interest rate: %.2f%%\n",5.25/12; # the value looks like "0.44%"

  • printf使用数组：

my @items = qw( wilma dino pebbles );              
my $format = "The items are:\n" . ("s\n" x @items);              
## print "the format is >>$format<<\n"; # for debugging                
printf $format, @items;