Reg Exp. Problem

[Joshila]

I need to write a regular expression which will match a string value for N's and T's but not a combination like NTNTNTN

This expression is what i wrote

[N*T*]$

Acceptable values of string
N
NNNNN.... any number of N's
T
TTTTTT ... any number of T's
N N N N there can be spaces inbetween
T T T T ...
but NOT something NTNTNTN or TNTNTNT
but the expression above is matching this combination tooo ...

Can anyone help me solve this?

[Elmar P. Kolkman]

Solution I would use: {N+|T+}$
It depends on the program you use if this is a supported regex. And use + instead of *, because you don't want to match empty patterns.

[Elmar P. Kolkman]

For egrep:
egrep 'N+$|T+$'

[Elmar P. Kolkman]

Sorry, missed one thing...
Should be:
egrep '^N+$|^T+$'