tariqahsan has asked for the wisdom of the Perl Monks concerning the following question:

I have a situation where I don't know how many variables and their values I would need to put in report. I am thinking of using the FORMAT template. Would anybody could know if I could dynamically create a FORMAT definition?

Replies are listed 'Best First'.
Re: Dynamically create a format definition
by jmcnamara (Monsignor) on Dec 13, 2001 at 19:54 UTC

    Have a look at the formline function and the accumulator $^A.

    Here is a short, seasonal, example that centres the elements of an array on separate lines. The format is built dynamically. 

    #!/usr/bin/perl -w

use strict;

my @a = qw(* *** ***** ******* ********* *);

formline(('@'.('|'x72)."\n")x@a, @a);
print $^A;

    [download]

    --
    John.

[reply]
[d/l]
Re: Dynamically creating a format definition?
by traveler (Parson) on Dec 13, 2001 at 20:58 UTC
    My second edition camel book shows how to do it. The critical points are: 1) put the output of the format statement into a variable, 2) eval that variable. Here is a piece of demonstration code. I have tried to make it readable, it is surely not the most compact version possible. 
    $data = qw( aaa bbb ccc );
$fields = scalar @data;
$data_fields = "";
map $data_fields .= '"' . $_ . '"', @data;
$format = "format STDOUT = \n"
        . "@<<< " x $fields . "\n"
        . $data_fields . "\n";
        . ".\n";
eval $format;
write;

    [download]
    HTH, --traveler
[reply]
[d/l]
Re: Dynamically create a format definition
by zakb (Pilgrim) on Dec 13, 2001 at 19:43 UTC
    Use eval. See the camel p 126 or perlform.
[reply]
Re: Dynamically create a format definition
by IlyaM (Parson) on Dec 13, 2001 at 20:28 UTC
    Here two functions I use myself in one my module: 
    
# formated output
sub sformat {
    my $format = shift;
    local $^A = '';
    formline($format, @_);
    return $^A;
}

# print line using some format specification
sub fprint {
    my $format = shift;
    $self->print(sformat($format, @_));
}

    [download]

    --
    Ilya Martynov (http://martynov.org/)

[reply]
[d/l]
Re: Dynamically create a format definition
by traveler (Parson) on Dec 13, 2001 at 21:09 UTC
[reply]

Back to Seekers of Perl Wisdom