plan9-sort(1) - sort and/or merge files
-M     Compare  as  months.   The first three non-white space characters of the field are folded to upper
       case and compared so that precedes etc.  Invalid fields compare low to
-b     Ignore leading white space (spaces and tabs) in field comparisons.
-d     `Phone directory' order: only letters, accented letters, digits and white space are significant in
-f     Fold  lower  case  letters  onto upper case.  Accented characters are folded to their non-accented
       upper case form.
-i     Ignore characters outside the ASCII range 040-0176 in non-numeric comparisons.
-w     Like -i, but ignore only tabs and spaces.
-n     An initial numeric string, consisting of optional white space, optional plus or  minus  sign,  and
       zero or more digits with optional decimal point, is sorted by arithmetic value.
-g     Numbers, like -n but with optional e-style exponents, are sorted by value.
-r     Reverse the sense of comparisons.
-tx    `Tab character' separating fields is x.

The  notation  +pos1 -pos2 restricts a sort key to a field beginning at pos1 and ending just before pos2.
Pos1 and pos2 each have the form m.n, optionally followed by one or more of the flags Mbdfginr,  where  m
tells  a  number  of  fields to skip from the beginning of the line and n tells a number of characters to
skip further.  If any flags are present they override all the global ordering options for  this  key.   A
missing .n means .0; a missing -pos2 means the end of the line.  Under the -tx option, fields are strings
separated by x; otherwise fields are non-empty strings separated by white space.  White  space  before  a
field  is  part of the field, except under option -b.  A b flag may be attached independently to pos1 and

The notation -k pos1[,pos2] is how POSIX sort defines fields: pos1 and pos2  have  the  same  format  but
different  meanings.   The value of m is origin 1 instead of origin 0 and a missing .n in pos2 is the end
of the field.

When there are multiple sort keys, later keys are compared only after all  earlier  keys  compare  equal.
Lines that otherwise compare equal are ordered with all bytes significant.

These option arguments are also understood:
-c         Check  that  the  single  input file is sorted according to the ordering rules; give no output
           unless the file is out of sort.
-m         Merge; assume the input files are already sorted.
-u         Suppress all but one in each set of equal lines.  Ignored bytes and bytes outside keys do  not
           participate in this comparison.
-o         The  next  argument is the name of an output file to use instead of the standard output.  This
           file may be the same as one of the inputs.
-Tdir      Put temporary files in dir rather than in /var/tmp.