use strict;
use warnings;

my $line = qq[file="path/goes/here"];

print "Line is '$line'\n";

if ($line =~ /^([^"]*)"([^"]*)"(.*)$/) {
    my ($prefix, $quoted, $suffix) = ($1, $2, $3);
    $quoted =~ s|[^/]|x|g;
    $line = qq[$prefix"$quoted"$suffix];
}

print "Line is '$line'\n";