If you are using whole files then we have GetFile and PutFile which do not require handles. Otherwise, a sys variable is used as a file handle:
use corewin
string s
sys e,f
'EQUIVALENT TO: S=GETFILE "T.TXT"
f=fopen "t.txt","r" 'open for reading
print f 'file handle or null
fseek f,0,2 'end of file
e=ftell f 'get position
print e 'length of file
fseek f,0,0 'beginning of file
s=nuls e 'create buffer to fit
fread s,1,e,f 'load buffer
fclose f 'close file