If no files are named, the standard input is sorted. The default sort key is an entire line. Default ordering is lexicographic by bytes in machine collating sequence. The ordering is affected globally by the following options, one or more of which may appear. The first three characters after optional white space are folded to lower case and compared.
Invalid fields compare low to jan .
Restrict the sort key to a string beginning at pos1 and ending at pos2 . If any flags are present they override all the global ordering options for this key. If pos2 is missing, it is taken to be end of line. The second form specifies fixed length records of reclen bytes. Keep only the first of two lines that compare equal on all keys.