a regex that does not contain comma

< ^ > P N |<>|^_>< --- | ~ ...Help

Hi
   Could anybody please tell how to write the validates_format_of a
string(in rails) which is only valid when it does not contain a
comma.For example

The are valid

hi welcome
Hello
h123 kk
hh gg hh

The are not valid

Hello,
Hi , world
Hello,welcome

Thanks in advnce
Sijo
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