Formatted Output with printf
You may wish to have a little more control with your output than
print provides. In fact, you may be
accustomed to the formatted output of C’s printf function. Fear not—Perl provides a
comparable operation with the same name.
The printf operator takes a
format string followed by a list of things to print. The format[†] string is a fill-in-the-blanks template showing the
desired form of the output:
printf "Hello, %s; your password expires in %d days!\n", $user, $days_to_die;
The format string holds a number of so-called
conversions; each conversion begins with a percent sign (%) and ends with a letter. (As we’ll see in a
moment, there may be significant extra characters between these two
symbols.) There should be the same number of items in the following list
as there are conversions; if these don’t match up, it won’t work
correctly. In the example above, there are two items and two
conversions, so the output might look something like this:
Hello, merlyn; your password expires in 3 days!
There are many possible printf
conversions, so we’ll take time here to describe just the most common
ones. Of course, the full details are available in the
perlfunc manpage.
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
The %d format means a
decimal[†] integer, truncated as needed:
printf "in %d days!\n", 17.85; ...