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
The sort command
Original author(s)Ken Thompson (AT&T Bell Laboratories)
Developer(s)Various open-source and commercial developers
Initial releaseNovember 3, 1971 (1971-11-03)
Operating systemMultics, Unix, Unix-like, V, Plan 9, Inferno, MSX-DOS, IBM i
PlatformCross-platform
TypeCommand
Licensecoreutils: GPLv3+

History

A sort command that invokes a general sort facility was first implemented within Multics.[1] 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.[2]

The version of sort bundled in GNU coreutils was written by Mike Haertel and Paul Eggert.[3] This implementation employs the merge sort algorithm.

Similar commands are available on many other operating systems, for example a sort command is part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.[4]

The sort command has also been ported to the IBM i operating system.[5]

Syntax

 
sort [OPTION]... [FILE]...

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

Parameters
Name Description Unix Plan 9 Inferno FreeBSD Linux MSX-DOS IBM i
-b,
--ignore-leading-blanks		 Ignores leading blanks. Yes Yes No Yes Yes No Yes
-c Check that input file is sorted. No Yes No Yes Yes No Yes
-C Like -c, but does not report the first bad line. No No No Yes Yes No No
-d,
--dictionary-order		 Considers only blanks and alphanumeric characters. Yes Yes No Yes Yes No Yes
-f,
--ignore-case		 Fold lower case to upper case characters. Yes Yes No Yes Yes No Yes
-g,
--general-numeric-sort,
--sort=general-numeric		 Compares according to general numerical value. Yes Yes No Yes Yes No No
-h,
--human-numeric-sort,
--sort=human-numeric		 Compare human readable numbers (e.g., 2K 1G). Yes No No Yes Yes No No
-i,
--ignore-nonprinting		 Considers only printable characters. Yes Yes No Yes Yes No Yes
-k,
--key=POS1[,POS2]		 Start a key at POS1 (origin 1), end it at POS2 (default end of line) No No No Yes Yes No No
-m Merge only; input files are assumed to be presorted. No Yes No Yes Yes No Yes
-M,
--month-sort,
--sort=month		 Compares (unknown) < 'JAN' < ... < 'DEC'. Yes Yes No Yes Yes No No
-n,
--numeric-sort,
--sort=numeric		 Compares according to string numerical value. Yes Yes Yes Yes Yes No Yes
-o OUTPUT Uses OUTPUT file instead of standard output. No Yes No Yes Yes No Yes
-r,
--reverse		 Reverses the result of comparisons. Yes Yes Yes Yes Yes No Yes
-R,
--random-sort,
--sort=random		 Shuffles, but groups identical keys. See also: shuf Yes No No Yes Yes No No
-s Stabilizes sort by disabling last-resort comparison. No No No Yes Yes No No
-S size,
--buffer-size=size		 Use size for the maximum size of the memory buffer. No No No Yes No No No
-tx 'Tab character' separating fields is x. No Yes No No Yes No Yes
-t char,
--field-separator=char		 Uses char instead of non-blank to blank transition. No No No Yes Yes No No
-T dir,
--temporary-directory=dir		 Uses dir for temporaries. No Yes No Yes Yes No No
-u,
--unique		 Unique processing to suppress all but one in each set of lines having equal keys. No Yes No Yes Yes No Yes
-V,
--version-sort		 Natural sort of (version) numbers within text No No No Yes Yes No No
-w Like -i, but ignore only tabs and spaces. No Yes No No No No No
-z,
--zero-terminated		 End lines with 0 byte, not newline No No No Yes Yes No No
--help Display help and exit No No No Yes Yes No No
--version Output version information and exit No No No Yes Yes No No
/R Reverses the result of comparisons. No No No No No Yes No
/S Specify the number of digits to determine how many digits of each line should be judged. No No No No No Yes No
/A Sort by ASCII code. No No No No No Yes No
/H Include hidden files when using wild cards. No No No No No Yes No

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 du command produces output that starts with a number, the file size, so its output can be piped to sort to produce a list of files sorted by (ascending) file size:

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

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 (+2 for the third, etc.). 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 (start at column m, end at column n):

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

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

Here the first sort is done using column 2. -k2,2 specifies sorting on the key starting and ending with column 2. 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. The n stands for 'numeric ordering'. -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[6][7] 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 (version) numbers within text. This happens to work for ip addresses.

See also

References
  1. "Multics Commands". www.multicians.org.
  2. McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.
  3. "sort(1): sort lines of text files - Linux man page". linux.die.net.
  4. "MSX-DOS2 Tools User's Manual - MSX-DOS2 TOOLS ユーザーズマニュアル". April 1, 1993 – via Internet Archive.
  5. IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). Retrieved 2020-09-05.
  6. "The GNU Bash Reference Manual, for Bash, Version 4.2: Section 3.1.2.4 ANSI-C Quoting". Free Software Foundation, Inc. 28 December 2010. Retrieved 1 February 2013. Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard.
  7. Fowler, Glenn S.; Korn, David G.; Vo, Kiem-Phong. "KornShell FAQ". Archived from the original on 2013-05-27. Retrieved 3 March 2015. The $'...' string literal syntax was added to ksh93 to solve the problem of entering special characters in scripts. It uses ANSI-C rules to translate the string between the '...'.

Further reading
  • Shotts (Jr), William E. (2012). The Linux Command Line: A Complete Introduction. No Starch Press. ISBN 978-1593273897.
  • McElhearn, Kirk (2006). The Mac OS X Command Line: Unix Under the Hood. John Wiley & Sons. ISBN 978-0470113851.
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