Harman Patil (Editor)

Sort (Unix)

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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.

Contents

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.

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:

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 to specify the tab as a C escape sequence.

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.

References

Sort (Unix) Wikipedia


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