$ostr = sprintf("$format", @stuff);
printf $ostr;
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That second printf is trying to do another interpolation. You want to use print here. Had you used warnings or if you ran your program using perl -w, Perl would raised at least a warning for the printf, even if that warning is misleading (in 5.10, fixed in 5.12 or at least 5.13.5):

> perl -wle "$f=sprintf'%-13s','%util';print $f;printf $f"
Use of uninitialized value $f in printf at -e line 1.
0til
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Of course, $f is not uninitialized, but there is no named variable anyway.