With Perl, we can format a number, character, string or text. We 
use line format for the text and printf format specifiers  
for the others. These specifiers are similar to those we use wiht C 
and Fortran languages.

1. The  printf format 
1.1. The specifiers
%c  character
%d 	decimal (integer) number (base 10)
%e 	exponential floating-point number
%f 	floating-point number
%i 	integer (base 10)
%o 	octal number (base 8)
%s 	a string of characters
%u 	unsigned decimal (integer) number
%x 	number in hexadecimal (base 16)
%% (or \% )	print a percent sign

1.1. The width of a number 
 
The statement:
printf("%x,ya", N);
means outputs the number N of thype "a" with "x+y" 
spaces and with "y" decimals 

Example1: Floating-point number
#!C:/Perl/bin/perl
use strict;
my $number = 12345.6789;
printf ("%5.3f",$number);# width of 8 with 3 decimals
printf ("\n");

printf ("'%14.5f'",$number); # quoted: 19 spaces with 5 decimals
printf ("\n");

printf ("%14.5f\n", - $number); # negative: width of 19 spaces with 5 decimals
 
The output is:
12345.679
'   12345.67890'
  -12345.67890
 
By default, these ouputs are right-justified. To left-justify those previous 
printf examples, just add a minus sign (-) after the % symbol:

Example:
#!C:/Perl/bin/perl
use strict;
my $number = 12345.6789;
printf ("%25.2f",$number);# width of 25 spaces and 2 decimals
printf ("\n");

printf ("%-25.2f",$number);# width of 25 spaces and 2 decimals
printf ("\n");

That output is:
                 12345.68
12345.68

  
Example2: integer number
#!C:/Perl/bin/perl
use strict;
my $number = 6789;
printf ("%3d",$number);# infeger: width of 3 spaces 
printf ("\n");

printf ("%6d",$number);# integer: width of 6 spaces 
printf ("\n");

# zero-fill option

printf ("%06d",$number);# integer: width of 6 spaces, zero-fill option
printf ("\n");

printf("'%-+5d'", $number); #quoted integer: width of 5 spaces

That output is:
6789
  6789
006789
'+6789'


Example3: Perl printf - printing strings

#!C:/Perl/bin/perl
use strict;
my $sentence = 'Astronauts walked on the moon in 1969.';
printf ("%s\n",$sentence);# as it is with new-line

printf ("'%s'",$sentence); # quoted
printf ("\n");

printf ("%44s",$sentence); # right-justified
printf ("\n");

printf ("'%- 44s'\n",$sentence); # quoted and left-justified with new-line

That output is:
Astronauts walked on the moon in 1969.
'Astronauts walked on the moon in 1969.'
      Astronauts walked on the moon in 1969.
'Astronauts walked on the moon in 1969.      '


2. Format and write
2.1. Using format and printf
With the acronym PERL(Practical Extraction and Reporting Language), Perl is 
then associated with parsing and manipulation files and data. Actually, reporting 
data outputs the formatted results to a file or STDOUT for examination.
Here are two ways to report results:

Example:
#!C:/Perl/bin/perl.exe -w
@Books= (
      "Physics:Waves:Michael Farady:324",
      "Mathematics:Trigonometry:Max Planck:453",
      "Chemistry:Molecules:Louis de Broglie:214",
	  "Geography:North America:Max Born:565",
      );
  printf "%-12s %-20s %-20s %3s\n", "Discipline", "Field", "Author", "Pages";
   printf "%-12s %-20s %-20s %3s\n", "----------", "-----", "------", "-----";
  foreach (@Books) {
      ($discipline, $field, $author, $pages) = split ":";
      $format = "%-12s %-20s %-20s %3d\n";
      printf  $format, $discipline, $field, $author, $pages;
  }

That output is:



2.2. Using format and write
Example:
#!C:/Perl/bin/perl.exe -w
@Books= (
      "Physics:Waves:Michael Farady:324",
      "Mathematics:Trigonometry:Max Planck:453",
      "Chemistry:Molecules:Louis de Broglie:214",
	  "Geography:North America:Max Born:565",
      );
  foreach (@Books) {
      ($discipline, $field, $author, $pages) = split ":";
	write;
  }
  # The headrer is written as:
  format STDOUT_TOP =
  Discipline   Field            Author     	     Pages
.
  format STDOUT =
  @<<<<<<<<<<< @<<<<<<<<<<<<<<< @<<<<<<<<<<<<<<<<<<< @>>
  $discipline,       $field,                                $author,    $pages
.
# The dot is very important.


 That output is: