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When you say cut an inmate, I am assuming you mean physically attacking an inmate with a knife? Be assured that you would face all the same charges as you would while on the outside. Not only: attempted murder (murder if the inmate is killed), aggravated battery, assault with a deadly weapon and armed criminal action.
On top of that, you would be faced with possession of the knife in a penal institution.
These are only the criminal charges that you would face, which would most likely run concurrent with whatever sentence you are currently under (assuming you are an inmate as well). Then you'll also have to deal with all administrative and department of corrections consequences which may follow (ie, loss of certain privileges or segregation from general population).
Hope I was able to answer your question.