my $set_password = '/usr/bin/ssh ' . $master_host . " 'echo \Q$new_password\E | /usr/bin/passwd --stdin \Q$username\E'"; 

##</code><code>##

my $master_host  = 'localhost';
my $username     = 'foo';
my $new_password = 'a\'b$c"d|e';

print "pwd: ",$new_password;

my $set_password = '/usr/bin/ssh ' . $master_host . " 'echo \Q$new_password\E | /usr/bin/passwd --stdin \Q$username\E'";

print "cmd: ",$set_password;
system $set_password;

__END__
pwd: a'b$c"d|e
cmd: /usr/bin/ssh localhost 'echo a\'b\$c\"d\|e | /usr/bin/passwd --stdin foo'
sh: Syntax error: Unterminated quoted string