AIX command to shift up

I would need the awk command or a better way to get my file that looks like

1234
5678
8912
3456
7890

to look like

1234,5678,8912,3456,7890

Thanks in advance

nawk -v ORS=, '{printf("%c%s", (FNR>1)?ORS:"",$0)}END{printf RS}' myFile

Thanks but the outcome is

,5678,8912,3456,7890

It missed the first line

Works just fine on Sun/Solaris.
Check you input once again - make sure the first line is not 'blank'.

Ok it works I was using the /usr/bin/nawk instead of the
/usr/xpg4/bin/awk