Why not try it and see?

>perl -wMstrict -e
"for (@ARGV) {
  my ($whole,$deci) = /(?:(\d*)\.?(\d+))|(?:(\d+)\.?(\d*))/;
  print qq({$_} {$whole} {$deci} \n)
  }
"   0.0   0.   0   .   X   .0   1.2   1.   1   .2
{0.0} {0} {0}
{0.} {} {0}
{0} {} {0}
Uninitialized value in concatenation (.) or string at -e line 1.
Uninitialized value in concatenation (.) or string at -e line 1.
{.} {} {}
Uninitialized value in concatenation (.) or string at -e line 1.
Uninitialized value in concatenation (.) or string at -e line 1.
{X} {} {}
{.0} {} {0}
{1.2} {1} {2}
{1.} {} {1}
{1} {} {1}
{.2} {} {2}
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(Uninitialized value messages truncated to avoid line wrap.)