web # perl -e '$a="nan"; print sprintf("%.2f",$a)'
nan

web # perl -v
This is perl, v5.8.8 built for x86_64-linux
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For Win32:
This is perl, v5.8.4 built for MSWin32-x86-multi-thread

perl -e "$a='nan'; print sprintf('%.2f',$a)"
0.00