The default sort key is an entire line. Default ordering is lexicographic by runes. The ordering is affected globally by the following options, one or more of which may appear.

-M

Compare as months. The first three non-white space characters of the field are folded to upper case and compared so that JAN precedes FEB, etc. Invalid fields compare low to JAN.

-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 comparisons.

-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 pos2.

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 /tmp.

sort -u +0f +0 list

Print in alphabetical order all the unique spellings in a list of words where capitalized words differ from uncapitalized.

sort -t: +1 /adm/users

Print the users file sorted by user name (the second colon-separated field).

sort -umM dates

Print the first instance of each month in an already sorted file. Options -um with just one input file make the choice of a unique representative from a set of equal lines predictable.

grep -n '^' input | sort -t: +1f +0n | sed 's/[0-9]*://' A stable sort: input lines that compare equal will come out in their original order.

Some of the options, e.g. -M, are hopelessly provincial.