仅将正则表达式替换应用于带引号的部分

 $in = \'ab  c \"d e  f\" g   h \"i    j\" k l\';
 #...?
 $inquotes =~ s/\\s+/_/g; #arbitrary regexp working only on the pieces inside quote marks
 #...?
 $out = \'ab  c \"d_e_f\" g   h \"i_j\" k l\';

\'ab  c d_e_f g

my $in = q(ab  c \"d e  f\" g   h \"i    j\" k l);

$in =~ s{\"(.+?)\"}{$1 =~ s/\\s+/_/gr}eg;
print \"$in\\n\";

split

join

my @pieces = split /\\\"/, $in, -1;

foreach my $i (0 ... $#pieces) {
    next unless $i % 2;
    $pieces[$i] =~ s/\\s+/_/g;
}

my $out = join \'\"\', @pieces;

s/\\\"([\\a\\w]*)\\\"/