Z:\>perl
use strict;

printf STDOUT "[%-20s] [%20s]\n", 1000 .. 1001;
^D
[1000                ] [                1001]

Z:\>
[download]

If you want to be strict about your columns, then you might need to trancate strings if they are longer than the width of the column. Your example can be changed like this:

Z:\>perl
use strict;

printf STDOUT "[%-20.20s] [%20.20s]\n", 1000 .. 1001;
^D
[1000                ] [                1001]

Z:\>
[download]

Leonid Mamtchenkov aka TVSET

The old-fashoned way to do this is with format, and it may be the best.

To do it with printf formats, you will need to construct the format string on the fly, taking account of the length of what you want to print.

Another way I'd consider is with substr:

my $line = ' ' x 200;
my $cols = {
    0    =>   \$var1,
    19   =>   \$var2,
    179  =>   \$var3,
    199  =>   \$var4
};
for (keys %$cols) {
    my $val = ${$cols->{$_}};
    substr $line, $_, length($val), $val;
}
print MERGE $line, $/;
[download]

Your $varN variables want to be an array, but I assume the names have been changed to protect the guilty ;-)

After Compline,
Zaxo

print MERGE pack('A20A180A200A350',@vars);
[download]

as for the faster part (I thought it would be a bigger difference):

#!/usr/local/bin/perl

use Benchmark;
use strict;

my $count = 10000;
my @lists = map { [chr($_+65),chr($_+66),chr($_+67),chr($_+68) ] } 0..
+22;

open(FH1,'>/tmp/x') or die "$!\n";
open(FH2,'>/tmp/y') or die "$!\n";

timethese ($count, { 'pack' => '&use_pack', 'printf' => '&use_printf' 
+} );

sub use_pack {
    foreach (@lists) {
        print FH1 pack('A20A180A200A350',@{$_});
    }
}

sub use_printf {
    foreach (@lists) {
        printf FH2 "%-20s%-180s%-200s%-350s", @{$_} ;
    }

}
[download]

Benchmark: timing 10000 iterations of pack, printf...
      pack: 21 wallclock secs (10.10 usr +  9.55 sys = 19.65 CPU) @ 50
+8.91/s (n=10000)
    printf: 24 wallclock secs (10.90 usr +  9.72 sys = 20.62 CPU) @ 48
+4.97/s (n=10000)

Benchmark: timing 10000 iterations of pack, printf...
      pack: 21 wallclock secs (10.03 usr +  9.75 sys = 19.78 CPU) @ 50
+5.56/s (n=10000)
    printf: 23 wallclock secs (11.88 usr + 10.72 sys = 22.60 CPU) @ 44
+2.48/s (n=10000)
[download]

You should never (well almost) write

 function( "$var")
[download]

 function( $var)
[download]

If you use the "$var" you are forcing Perl to convert the value of $var to a string and create a copy. This is usualy just a waste of time and memory, but sometimes it actualy breaks the code. If the $var is a reference (or an object ... which is actually also a reference) then Perl creates a string that looks like SCALAR(0x1a4b680). But there is no way to convert this back to a reference. So instead of passing the reference or object you pass a completely useless string.

Jenda
Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.
   -- Rick Osborne

Edit by castaway: Closed small tag in signature