-c

Checks that the single input file is ordered as specified by the arguments and the collating sequence of the current locale. The exit code is set and no output is produced unless the file is out of sort.

-c

Same as /usr/bin/sort except no output is produced under any circumstances.

-m

Merges only. The input files are assumed to be already sorted.

-o output

Specifies the name of an output file to be used instead of the standard output. This file can be the same as one of the input files.

-S kmem

Specifies the maximum amount of swap-based memory used for sorting, in kilobytes (the default unit). kmem can also be specified directly as a number of bytes (b), kilobytes (k), megabytes (m), gigabytes (g), or terabytes (t); or as a percentage (%) of the installed physical memory.

-T directory

Specifies the directory in which to place temporary files.

-u

Unique: suppresses all but one in each set of lines having equal keys. If used with the -c option, checks that there are no lines with duplicate keys in addition to checking that the input file is sorted.

-y kmem

(obsolete). This option was used to specify the amount of main memory initially used by sort. Its functionality is not appropriate for a virtual memory system; memory usage for sort is now specified using the -S option.

-z recsz

(obsolete). This option was used to prevent abnormal termination when lines longer than the system-dependent default buffer size are encountered. Because sort automatically allocates buffers large enough to hold the longest line, this option has no effect.

The default sort order depends on the value of LC_COLLATE. If LC_COLLATE is set to C, sorting will be in ASCII order. If LC_COLLATE is set to en_US, sorting is case insensitive except when the two strings are otherwise equal and one has an uppercase letter earlier than the other. Other locales will have other sort orders.

The following options override the default ordering rules. When ordering options appear independent of any key field specifications, the requested field ordering rules are applied globally to all sort keys. When attached to a specific key (see Sort Key Options), the specified ordering options override all global ordering options for that key. In the obsolescent forms, if one or more of these options follows a +pos1 option, it will affect only the key field specified by that preceding option.

-d

``Dictionary'' order: only letters, digits, and blanks (spaces and tabs) are significant in comparisons.

-f

Folds lower-case letters into upper case.

-i

Ignores non-printable characters.

-M

Compares as months. The first three non-blank characters of the field are folded to upper case and compared. For example, in English the sorting order is "JAN" < "FEB" < ... < "DEC". Invalid fields compare low to "JAN". The -M option implies the -b option (see below).

-n

Restricts the sort key to an initial numeric string, consisting of optional blank characters, optional minus sign, and zero or more digits with an optional radix character and thousands separators (as defined in the current locale), which will be sorted by arithmetic value. An empty digit string is treated as zero. Leading zeros and signs on zeros do not affect ordering.

-r

Reverses the sense of comparisons.

The treatment of field separators can be altered using the following options:

-b

Ignores leading blank characters when determining the starting and ending positions of a restricted sort key. If the -b option is specified before the first sort key option, it is applied to all sort key options. Otherwise, the -b option can be attached independently to each -k field_start, field_end, or +pos1 or -pos2 option-argument (see below).

-t char

Use char as the field separator character. char is not considered to be part of a field (although it can be included in a sort key). Each occurrence of char is significant (for example, <char><char> delimits an empty field). If -t is not specified, blank characters are used as default field separators; each maximal non-empty sequence of blank characters that follows a non-blank character is a field separator.

Sort keys can be specified using the options:

-k keydef

The keydef argument is a restricted sort key field definition. The format of this definition is:

-k field_start [type] [,field_end [type] ]

where:

field_start and field_end

define a key field restricted to a portion of the line.

type

is a modifier from the list of characters bdfiMnr. The b modifier behaves like the -b option, but applies only to the field_start or field_end to which it is attached and characters within a field are counted from the first non-blank character in the field. (This applies separately to first_character and last_character.) The other modifiers behave like the corresponding options, but apply only to the key field to which they are attached. They have this effect if specified with field_start, field_end or both. If any modifier is attached to a field_start or to a field_end, no option applies to either.

When there are multiple key fields, later keys are compared only after all earlier keys compare equal. Except when the -u option is specified, lines that otherwise compare equal are ordered as if none of the options -d, -f, -i, -n or -k were present (but with -r still in effect, if it was specified) and with all bytes in the lines significant to the comparison.

The notation:

-k field_start[type][,field_end[type]]

defines a key field that begins at field_start and ends at field_end inclusive, unless field_start falls beyond the end of the line or after field_end, in which case the key field is empty. A missing field_end means the last character of the line.

A field comprises a maximal sequence of non-separating characters and, in the absence of option -t, any preceding field separator.

The field_start portion of the keydef option-argument has the form:

field_number[.first_character]

Fields and characters within fields are numbered starting with 1. field_number and first_character, interpreted as positive decimal integers, specify the first character to be used as part of a sort key. If .first_character is omitted, it refers to the first character of the field.

The field_end portion of the keydef option-argument has the form:

field_number[.last_character]

The field_number is as described above for field_start. last_character, interpreted as a non-negative decimal integer, specifies the last character to be used as part of the sort key. If last_character evaluates to zero or .last_character is omitted, it refers to the last character of the field specified by field_number.

If the -b option or b type modifier is in effect, characters within a field are counted from the first non-blank character in the field. (This applies separately to first_character and last_character.)

[+pos1 [-pos2]]

(obsolete). Provide functionality equivalent to the -kkeydef option.

pos1 and pos2 each have the form m.n optionally followed by one or more of the flags bdfiMnr. A starting position specified by +m.n is interpreted to mean the n+1st character in the m+1st field. A missing .n means .0, indicating the first character of the m+1st field. If the b flag is in effect n is counted from the first non-blank in the m+1st field; +m.0b refers to the first non-blank character in the m+1st field.

A last position specified by -m.n is interpreted to mean the nth character (including separators) after the last character of the mth field. A missing .n means .0, indicating the last character of the mth field. If the b flag is in effect n is counted from the last leading blank in the m+1st field; -m.1b refers to the first non-blank in the m+1st field.

The fully specified +pos1 -pos2 form with type modifiers T and U:

+w.xT -y.zU

is equivalent to:

undefined (z==0 & U contains b & -t is present) -k w+1.x+1T,y.0U (z==0 otherwise) -k w+1.x+1T,y+1.zU (z > 0)

Implementations support at least nine occurrences of the sort keys (the -k option and obsolescent +pos1 and -pos2) which are significant in command line order. If no sort key is specified, a default sort key of the entire line is used.

Either of the following commands sorts the contents of infile with the second field as the sort key:

example% sort -k 2,2 infile
example% sort +1 -2 infile 

Either of the following commands sorts, in reverse order, the contents of infile1 and infile2, placing the output in outfile and using the second character of the second field as the sort key (assuming that the first character of the second field is the field separator):

example% sort -r -o outfile -k 2.2,2.2 infile1 infile2 
example% sort -r -o outfile +1.1 -1.2 infile1 infile2

Either of the following commands sorts the contents of infile1 and infile2 using the second non-blank character of the second field as the sort key:

example% sort -k 2.2b,2.2b infile1 infile2 
example% sort +1.1b -1.2b infile1 infile2

Either of the following commands prints the passwd(4) file (user database) sorted by the numeric user ID (the third colon-separated field):

example% sort -t : -k 3,3n /etc/passwd 
example% sort -t : +2 -3n /etc/passwd

Either of the following commands prints the lines of the already sorted file infile, suppressing all but one occurrence of lines having the same third field:

example% sort -um -k 3.1,3.0 infile 
example% sort -um +2.0 -3.0 infile 

Either of the following commands prints the hosts(4) file (IPv4 hosts database), sorted by the numeric IP address (the first four numeric fields):

example$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n /etc/hosts
example$ sort -t . +0 -1n +1 -2n +2 -3n +3 -4n /etc/hosts

Since '.' is both the field delimiter and, in many locales, the decimal separator, failure to specify both ends of the field will lead to results where the second field is interpreted as a fractional portion of the first, and so forth.