Sort (Unix)

In computing, sort is a standard command line program of Unix and Unix-like operating systems, that prints the lines of its input or concatenation of all files listed in its argument list in sorted order. Sorting is done based on one or more sort keys extracted from each line of input. By default, the entire input is taken as sort key. Blank space is the default field separator. The command supports a number of command-line options that can vary by implementation. For instance the "-r" flag will reverse the sort order. Sort ordering is affected by the environment's locale settings.

History

A command that invokes a general sort facility was first implemented within Multics. Later, it appeared in Version 1 Unix. This version was originally written by Ken Thompson at AT&T Bell Laboratories. By Version 4 Thompson had modified it to use pipes, but sort retained an option to name the output file because it was used to sort a file in place. In Version 5, Thompson invented "-" to represent standard input.
is part of X/Open Portability Guide Issue 2. From there it was inherited into POSIX.
The version of bundled in GNU coreutils was written by Mike Haertel and Paul Eggert. This implementation employs the mergesort algorithm. It offers an option to sort in parallel, though performance gain diminishes after 8 threads. GNU parallel also provides a wrapper to perform parallel invocations of with similar performance-gain characteristics: on a 48-core system, the speedup is about 3×.
The command has also been ported to the IBM i operating system, being accessible from the POSIX-compatible Qshell.

Non-POSIX ports

Similar commands are available on many other operating systems, for example a command is part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.
The "uutils" project provides a cross-platform implementation of written in Rust, with support for all of GNU coreutil's options. It uses the or function of Rayon, the Rust multi-threading library, implementing either an adaptive mergesort inspired by timsort or a variation of pattern-defeating quicksort.

Syntax

sort ... ...
With no FILE, or when FILE is -, the command reads from standard input.

Parameters

In the table below, "Short" indicates only support for the one-letter form of the option. Long options are originally a GNU extension and is not part of any version of SUS or POSIX. It has since also been adopted by FreeBSD.

Name	Description	SUS/POSIX	Plan 9	Inferno	FreeBSD	Linux	MSX-DOS	IBM i
,	roIgnores leading blanks.
,	Check that input file is sorted.
,	Like -c, but does not report the first bad line.
,	Considers only blanks and alphanumeric characters.
,	Fold lower case to upper case characters.
, ,	Compares according to general numerical value.
, ,	Compare human readable numbers.
,	Considers only printable characters.
, POS1''POS2	Start a key at POS1, end it at POS2
	Merge only; input files are assumed to be presorted.
, ,	Compares < 'JAN' <... < 'DEC'.
, ,	Compares according to string numerical value.
OUTPUT	Uses OUTPUT file instead of standard output.
,	Reverses the result of comparisons.
, ,	Shuffles, but groups identical keys. See also: shuf
	Stabilizes sort by disabling last-resort comparison.
size, size	Use size for the maximum size of the memory buffer.
char, char	Uses char instead of non-blank to blank transition. In other words, 'Tab character' separating fields is char.
dir, dir	Uses dir'' for temporaries.
,	Unique processing to suppress all but one in each set of lines having equal keys.
,	Natural sort of numbers within text
	Like -i, but ignore only tabs and spaces.
,	End lines with 0 byte, not newline
	Display help and exit
	Output version information and exit
	Reverses the result of comparisons.
	Specify the number of digits to determine how many digits of each line should be judged.
	Sort by ASCII code.
	Include hidden files when using wild cards.

Examples

Sort a file in alphabetical order

$ cat phonebook
Smith, Brett 555-4321
Doe, John 555-1234
Doe, Jane 555-3214
Avery, Cory 555-4132
Fogarty, Suzie 555-2314

$ sort phonebook
Avery, Cory 555-4132
Doe, Jane 555-3214
Doe, John 555-1234
Fogarty, Suzie 555-2314
Smith, Brett 555-4321

Sort by number

The -n option makes the program sort according to numerical value. The command produces output that starts with a number, the file size, so its output can be piped to to produce a list of files sorted by file size:

$ du /bin/* | sort -n
4 /bin/domainname
24 /bin/ls
102 /bin/sh
304 /bin/csh

The command with the option prints file sizes in the 7th field, so a list of the files sorted by file size is produced by:

$ find. -name "*.tex" -ls | sort -k 7n

Columns or fields

Use the -k option to sort on a certain column. For example, use "-k 2" to sort on the second column. In old versions of sort, the +1 option made the program sort on the second column of data. This usage is deprecated.

$ cat zipcode
Adam 12345
Bob 34567
Joe 56789
Sam 45678
Wendy 23456

$ sort -k 2n zipcode
Adam 12345
Wendy 23456
Bob 34567
Sam 45678
Joe 56789

Sort on multiple fields

The -k m,n option lets you sort on a key that is potentially composed of multiple fields :

$ cat quota
fred 2000
bob 1000
an 1000
chad 1000
don 1500
eric 500

$ sort -k2,2n -k1,1 quota
eric 500
an 1000
bob 1000
chad 1000
don 1500
fred 2000

Here the first sort is done using column 2. -k2,2n specifies sorting on the key starting and ending with column 2, and sorting numerically. If -k2 is used instead, the sort key would begin at column 2 and extend to the end of the line, spanning all the fields in between. -k1,1 dictates breaking ties using the value in column 1, sorting alphabetically by default. Note that bob, and chad have the same quota and are sorted alphabetically in the final output.

Sorting a pipe delimited file

$ sort -k2,2,-k1,1 -t'|' zipcode
Adam|12345
Wendy|23456
Sam|45678
Joe|56789
Bob|34567

Sorting a tab delimited file

Sorting a file with tab separated values requires a tab character to be specified as the column delimiter. This illustration uses the shell's dollar-quote notation
to specify the tab as a C escape sequence.

$ sort -k2,2 -t $'\t' phonebook
Doe, John 555-1234
Fogarty, Suzie 555-2314
Doe, Jane 555-3214
Avery, Cory 555-4132
Smith, Brett 555-4321

Sort in reverse

The -r option just reverses the order of the sort:

$ sort -rk 2n zipcode
Joe 56789
Sam 45678
Bob 34567
Wendy 23456
Adam 12345

Sort in random

The GNU implementation has a -R --random-sort option based on hashing; this is not a full random shuffle because it will sort identical lines together. A true random sort is provided by the Unix utility shuf.

Sort by version

The GNU implementation has a -V --version-sort option which is a natural sort of numbers within text. Two text strings that are to be compared are split into blocks of letters and blocks of digits. Blocks of letters are compared alpha-numerically, and blocks of digits are compared numerically. Blocks are compared left-to-right and the first non-equal block in that loop decides which text is larger. This happens to work for IP addresses, Debian package version strings and similar tasks where numbers of variable length are embedded in strings.