$ perl -E '
$val = q{2.73M};
%exp = ( M => 6 );
$val =~ s/\d(\w)/exists $exp{ $1 } ? q{e} . $exp{ $1 } : q{} /e;
say $val;'
2.M
$ perl -E '
$val = q{2.73M};
%exp = ( M => 6 );
$val =~ s/(?<=\d)(\w)/exists $exp{ $1 } ? q{e} . $exp{ $1 } : q{} /e;
say $val;'
2.7M
$ perl -E '
$val = q{2.73M};
%exp = ( M => 6 );
$val =~ s/(?<=\d)([TGMkmunp])/exists $exp{ $1 } ? q{e} . $exp{ $1 } : q{} /e;
say $val;'
2.73e6
~ $