C:\_64\strawberry5.24.1>perl -e"CORE::say sprintf '%.20g', 0.1"
0.10000000000000001

C:\_64\strawberry5.24.1>

##</code><code>##

C:\>perl -MMath::MPFR=":mpfr" -le "$x=Math::MPFR->new('0.1'); $base=10; $digits=20; Rmpfr_out_str($x, $base, $digits, MPFR_RNDN);"
1.0000000000000000555e-1
C:\>

##</code><code>##

C:\>perl -e"CORE::say sprintf '%.20g', 0.1"
0.10000000000000000555

C:\>