The Perl printf is much like the printf
function in C and awk in that it takes a string to be formatted
and a list of format arguments, applies the formatting to the
string, and then typically prints the formatted string to
standard output, which in our case, is the Web browser.
The printf syntax uses a double quoted
string which includes special format markers followed by a
comma-delimited list of arguments to be applied to those markers.
The format markers are typically in the form of a percent sign
followed by a control character.
For example, the generic format of
printf might look like the following code:
printf ("[some text] %[format] [other text]",
[argument to be formatted]);
In usage, we might use the %s formatting
argument specifying a string and the %d formatting argument
specifying a digit using the following syntax:
#!/usr/local/bin/perl
print "Content-type: text/html\n\n";
$name = "Selena Sol";
$age = 28;
printf ("My name is %s and my age is %d.\n",
$name, $age);
The code above would produce the
following output in the Web browser window:
My name is Selena Sol and my age is 28.
In reality, the printf function is
rarely used in Perl CGI since, unlike C which almost demands the
use of printf, Perl has much easier ways of printing. However,
the printf routines are essential for another, more useful
(to CGI developers) function, sprintf.
Unlike printf, sprintf takes the
formatted output and assigns it to a variable rather than
outputting it to standard output (<STDOUT>), using the
following generic syntax:
$variable_name = sprintf ("[some text]
%[format] [other text]", [string to be
formatted]);
A good example of using sprintf might
come from a shopping cart script. In this script, we need to
format subtotals and grand totals to two decimal places so that
prices come out to numbers like "$99.00" or "$98.99" rather than
"99" or "98.99876453782". Below is a snippet of code which uses
sprintf to format a price string to two decimal places.
$option_grand_total = sprintf ("%.2f\n",
$unformatted_option_grand_total);
In this example, the variable,
$unformatted_option_grand_total is formatted using the "%.2f"
argument which formats (%) the string to two decimal places
(.2f).
There are a multitude of formatting
arguments besides "%s", "%d" and "%f", however. The following
Table lists several useful ones.
