By using a sprintf parameter to determine the width:

my $str = '1234567890' x 6;
my $prefixLen;
my $magicLimit = tie_me_a_scalar(sub { $max_width - $prefixLen });

printf "Prefix stuff %n%.*s", $prefixLen, $magicLimit, $str;

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Update: corrected %*s to %.*s

In reply to Re^4: How to use sprintf %n formatting pattern by hv
in thread How to use sprintf %n formatting pattern by ibm1620

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