I want to print a record with 5 fields, truncating the final one if necessary to prevent its wrapping at the edge of the terminal window, whose width is $max_width.

For example, if max_width = 60: 

1.......10........20........30........40........50........60
79.30 2022/1/8  The quick brown fox jumps over the lazy dog|
394571.00 22/10/81  The quick brown fox jumps over the lazy|
123456.78 12345/123/1234  The quick brown fox jumps over th|

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The printf pattern %n "*stores* the number of characters output so far into the next argument in the parameter list." That sounds like part of the solution (max_width - n would be the remaining space on the line and the length to which to truncate the final argument with a %-.*s construct) but I can't see any way to perform a calculation on the value that %n inserts.

Here's the code I've written, with the truncation value manually calculated: 

#!/usr/bin/env perl
use 5.010;
use warnings;
use strict;

my $max_width = 60;
my $scale = '1.......10........20........30........40........50.......
+.60';
my $long_string = q{The quick brown fox jumps over the lazy dog};
my $pat = "%.2f %d/%d/%d  %-.*s|\n";
my @aoa = (
    [ qw/79.3      2022  1   8    43/, $long_string ],
    [ qw/394571    22    10  81   39/, $long_string ],
    [ qw/123456.78 12345 123 1234 33/, $long_string ],
    #                    compute  ^^  as (60 - pos)
);

say $scale;
for my $aref (@aoa) {
    printf( $pat, @$aref );
}

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I can't easily imagine why the %n value itself would be useful except as part of some calculation. Any clarification would be much appreciated!

In reply to How to use sprintf %n formatting pattern by ibm1620

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