Formats in Perl

Last Updated : 12 Jul, 2025

Formats are the writing templates used in Perl to output the reports. Perl has a mechanism which helps in generating simple reports and charts. Instead of executing, Formats are declared, so they may occur at any point in the program. Formats have their own namespace apart from the other types in Perl i.e. function named "tron" is not same as format named "tron". However, name of the filehandle in the program is the default name for the format associated with that filehandle.

Defining a Format

Syntax to define a Perl Format:

format FormatName =
fieldline
value_1, value_2, value_3
fieldline
value_1, value_2, value_3
.

- Name of the format is denoted by the FormatName. - Fieldline is a particular way used to format the data. Fieldline can also hold text or fieldholders. - Value lines denotes/describes the values which will be entered into the fieldlines. - Format is ended by a single period (.) - Fieldholders have the space for the data which will be entered later. Syntax for Fieldholders:

@<<<<<<<       left-justified (with 7 field spaces by counting '@' and '<')
@|||||||       center-justified
@###.####      numeric fieldholder
@*             multiline fieldholder

Using a Format

Write keyword is used to call on the format declaration.

Write FormatName;

Format name is the name of an open file handle and the write statement sends the output to the same file handle. In order to send the data to STDOUT, format name needs to be associated with the STDOUT file handle. Note: Use the select() function for making sure that STDOUT is the selected file handle.

select (STDOUT);

In order to associate format name with STDOUT by setting the new format name with STDOUT, use the variables like $~ or $Format_Name

$~ = "Format_Name";

Note: For writing report in any other file handle apart from the STDOUT, use the select() function to select that file handle. Example: Input: Using STDOUT.

Perl

#!/usr/bin/perl
print "Content-type: text/html\n\n";
 
@First_Name = qw(Karthik Raman Shivam Tarun);
@Last_Name = qw(Singh Biswas Anand Mishra);
@ID = qw(101 186 009 359);
@Phone_Number = qw(963x 885x 734x 921x);
 
format DATA = 
@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<
$First_Name[$k] $Last_Name[$k]  $ID[$k]         $Phone_Number[$k]
 
.
 
select(STDOUT);
$~ = DATA;
$k = 0;
while ($k <= $#First_Name)
{
    write;
    $k++;
}

Output :

Input: Using other file handle(Printing the output into a text file.)

Perl

#!/usr/bin/perl

print "Content-type: text/html\n\n";


@First_Name = qw(Karthik Raman Shivam Tarun);
@Last_Name = qw(Singh Biswas Anand Mishra);
@ID = qw(101 186 009 359);
@Phone_Number = qw(963x 885x 734x 921x);


format DATA = 
@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<
$First_Name[$k] $Last_Name[$k]  $ID[$k]         $Phone_Number[$k]

.

open(FILE, ">file.txt");
select FILE;
$~ = DATA;

$k = 0;
while ($k <= $#First_Name)
{
    write;
    $k++;
}

close FILE;

Output :

File where data is printed:

Report Header and Footer

Header is something that appears at the top of each page. Instead of defining a template, just define a header and assign it to $^ or $FORMAT_NAME_TOP. Footer has a fixed size. It can be achieved by checking for variable $-. You can even print the footer by yourself if necessary using the syntax given below,

format FORMAT_NAME_BOTTOM
End of Page $%

Example: Input: Using STDOUT

Perl

#!/usr/bin/perl
print "Content-type: text/html\n\n";
 
format DATA_TOP = 
@||||||||||||||||||||||||||||||||||||||||||||||||||||
                  "Staff Members"
               ----------------------
First           Last            ID              Phone
------------------------------------------------------
.
 
@First_Name = qw(Karthik Raman Shivam Tarun);
@Last_Name = qw(Singh Biswas Anand Mishra);
@ID = qw(101 186 009 359);
@Phone_Number = qw(963x 885x 734x 921x);
 
format DATA = 
@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<
$First_Name[$k] $Last_Name[$k]  $ID[$k]         $Phone_Number[$k]
 
.
 
select (STDOUT);
$~ = DATA;
$^ = DATA_TOP;
$k = 0;
while ($k <= $#First_Name)
{
    write;
    $k++;
}

Output:

Input: Getting output into a text file.

Perl

#!/usr/bin/perl
print "Content-type: text/html\n\n";

format DATA_TOP = 
@||||||||||||||||||||||||||||||||||||||||||||||||||||
                  "Staff Members"
               ----------------------
First           Last            ID              Phone
------------------------------------------------------
.

@First_Name = qw(Karthik Raman Shivam Tarun);
@Last_Name = qw(Singh Biswas Anand Mishra);
@ID = qw(101 186 009 359);
@Phone_Number = qw(963x 885x 734x 921x);


format DATA = 
@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<
$First_Name[$k] $Last_Name[$k]  $ID[$k]         $Phone_Number[$k]

.

open (FILE, ">file.txt");
select FILE;
$~ = DATA;
$^ = DATA_TOP;

$k = 0;
while ($k <= $#First_Name)
{
    write;
    $k++;
}
close FILE;

Output:

File where data is printed:

Pagination

Pagination comes into the picture when you have a long report which will not fit in a single page. Use of variables like $% or $FORMAT_PAGE_NUMBER along with the header in the format helps in defining the page number to more than one page. Default number of lines in a page is 60 but it can be set manually too by using the variables $= or $FORMAT_LINES_PER_PAGE. Example:

Perl

#!/usr/bin/perl
print "Content-type: text/html\n\n";

format DATA_TOP = 
@>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
"[Page $%]"
@||||||||||||||||||||||||||||||||||||||||||||||||||||
                  "Staff Members"
               ----------------------
First           Last            ID              Phone
------------------------------------------------------
.

@First_Name = qw(Karthik Raman Shivam Tarun);
@Last_Name = qw(Singh Biswas Anand Mishra);
@ID = qw(101 186 009 359);
@Phone_Number = qw(963x 885x 734x 921x);


format DATA = 
@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<@<<<<<<<<<<<<<<<
$First_Name[$k] $Last_Name[$k]  $ID[$k]         $Phone_Number[$k]

.

select (STDOUT);
$~ = DATA;
$^ = DATA_TOP;
$= = 1;

$k = 0;
while ($k <= $#First_Name)
{
    write;
    $k++;
}