sort - sort lines in a stream¶

The sort program takes lines of text as input and outputs the text in alphabetical-sorted order.

To sort the lines in a file:

$ sort fruits.txt

The most common use, though, is to sort lines from standard inpput, piped in from another program:

$ curl http://2017.compciv.org/_downloads/fruits.txt | sort

Use-cases¶

Sorting in reverse¶

If you want the list of sorted lines to be in descending order, i.e. z before a, use the -r flag:

$ sort -r fruits.txt

Sorting numbers¶

By default, sort sorts alphabetically. When numbers are treated as just characters, then 100 will be less than 9.

Given this list of numbers:

The default sorting behavior will result in:

Using the -n flag will force sort to rank numerical characters by their numerical order:

$ sort -n numbers.txt

The result:

Sorting in reverse numerical order¶

A very common use-case is to sort a list of numbers in reverse-order, i.e. biggest on top. You can call sort with both the -r and the -n flags:

$ sort -r -n numbers.txt

# alternatively, you can combine the flags like this:

$ sort -rn numbers.txt

A very common question is to look for the “Top N” of a sorted list. So pipe sort into head.

The following example reads the data from a remote URL via curl, pipes it into sort, and finally into head to show only the top 5 numbers

$ curl http://2017.compciv.org/_downloads/numbers.txt \
    | sort -rn \
    | head -n 5

A necessary step before uniq¶

The uniq program is a nice example of a Unix program that does something very focused: it takes in a stream of lines, and outputs just the unique lines. But it can do this unique/grouping comparison line-by-line. In other words, if you feed it a file in which “apples” is the first line and “apples” is the last line, and there are a bunch of non-“apples” lines in between, uniq will not know that apples was duplicated.

In order to get the intended effect of uniq, sort is used to sort the lines of text before piping into uniq:

$ curl http://2017.compciv.org/_downloads/fruits.txt | sort | uniq

Sorting by most frequent occurrences¶

The sort program, in modern implementations, does have a -u flag that effectively does the uniq function, without actually having to call uniq:

$ curl http://2017.compciv.org/_downloads/fruits.txt | sort -u