c# - Match all words from given string where words does not have only lower case letters or only upper case letters -

i retrieve words given string not caps , lower or first letter upper

for example in below sentence should extracted except first 4 words:

a abcd hello ajp

string str = "a abcd hello ajp lbl_description mhz assignexistinguseroptiontext _bthaudclassdrv_keyword a_dd actelismetaloop audenginestream_beginstreamswitch_enter audenginestream_begineos bo_th btnchange c_hange cds check_and_change_access_masks checkbox1 cimobjectpath ciscoislvlan comboemailaccounts d_elete csvfs_refs d_hcp dadornudreply decnet ipv4 kj kpa lalt  ml n_o tabpage11 uapsd vlans ycbcr" 

you can using split method , linq:

var result = str.split(new[] {' '}, stringsplitoptions.removeemptyentries)                 .where(x => !x.all(char.isupper) &&                             !x.all(char.islower) &&                             !(char.isupper(x[0]) &&                               x.skip(1).all(char.islower)))                 .toarray();