There are no functions in matlab to calculate hashes. However, you can call Java (any OS) or .Net (Windows only) functions directly from matlab and either of these implement what you want.
Note that you haven't specified the encoding of the string. The hash is different if you consider the string in ASCII, UTF8, UTF16, etc.
Also note that matlab does not have 160-bit or 256-bit integer, so the hash can't obviously be a single integer.
Anyway, using .Net:
string = 'some string';
sha256hasher = System.Security.Cryptography.SHA256Managed;
sha256 = uint8(sha256hasher.ComputeHash(uint8(string)));
sha1hasher = System.Security.Cryptography.SHA1Managed;
If you want to use Java you'll have to figure out that for yourself.