fmgr, C , and character arguments

Hello all,
I am having a bit of trouble getting my arguments formatted into a
command string for system(). Here is what I have so far for code.

#include <string.h>
#include <stdlib.h>
#include "postgres.h"
#include "fmgr.h"


PG_FUNCTION_INFO_V1(ssh_exec);

Datum
ssh_exec(PG_FUNCTION_ARGS)
{
char *uname = PG_GETARG_CHAR(0);
char *uid = PG_GETARG_CHAR(1);
char *gid = PG_GETARG_CHAR(2);

strncpy(sshcmd, "/usr/local/bin/plsshexec ", 255);
strncat(sshcmd, *uname, 255);
strncat(sshcmd, " ", 255);
strncat(sshcmd, *uid, 255);
strncat(sshcmd, " ", 255);
strncat(sshcmd, *gid, 255);
system(sshcmd);
return 0;
}

I am thinking that strncpy is not a bad idea after moving to the V-1
function manager interface. As I am sure you can see I am a C hack at best.
what is the best way to format the string and make this code work? memcpy?
Thanks for reading my post.

- Joel