-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.