sort (Unix)

In Unix-like operating systems, sort is a standard command line program 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 "-r" flag will reverse the sort order.

History

Sort was part of Version 1 Unix. By Version 4 Ken 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.[1]

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 5000

$ sort -k2,2 -k1,1 quota
an 1000
bob 1000
chad 1000
don 1500
fred 2000
eric 5000

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, an and chad have the same quota and are sorted alphabetically in the final output.

Sorting a pipe delimited file 

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

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[2][3] 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.

Sorting algorithm

The implementation in GNU Core Utilities, used on Linux, employs the merge sort algorithm.

See also

References

  1. ↑ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.
  2. ↑ "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.
  3. ↑ 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 '...'.
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