sort.md

sort

sort is a command-line tool with a robust set of uses, though the basic usage is to sort various types of input.

Lexicographic Sorts

At its core sort is a tool that sorts input into lexicographical or numerical order. By default, sort orders the input into ascending order.

$ printf "cat\ngnat\nmat\nbat\ntat" | sort
bat
cat
gnat
mat
tat

The -f option can be provided to ignore casing.

$ printf "cat\nGnat\nmat\nBat\ntat" | sort -f
Bat
cat
Gnat
mat
tat

The -d option can be provided to only consider alphabetical, numerical, and spacing characters in sorting.

$ printf "(cat)\ngnat\n(mat)\n[bat]\ntat" | sort -d
[bat]
(cat)
gnat
(mat)
tat

The -i option can be provided to further expand the set of characters considered in sorting to only printable characters.

The -r option can be provided to reverse the output order. Note that this does not change how the comparisons are performed, it merely outputs the results in reversed order.

$ printf "cat\ngnat\nmat\nbat\ntat" | sort -r    
tat
mat
gnat
cat
bat

Numerical Sorts

Providing the -n option to sort will handle most numerical sorts.

# lexicographic sorts do not work for numbers
$ printf "2\n20\n12\n123" | sort
12
123
2
20

# -n works for sorting these though
$ printf "2\n20\n12\n123" | sort -n
2
12
20
123

By default, the -n option automatically handles negative and floating-point numbers. Note that parsing the decimal and thousands separators will depend on the locale settings.

$ printf "3.14\n-12.34\n214\n-1234\n45" | sort -n
-1234
-12.34
3.14
45
214

The -g option can be provided to properly sort numbers that are preceeded with a + or are in E scientific notation.

$ printf "+3.14\n-1.234e-2\n2.14e+2\n-1234\n+45" | sort -g
-1234
-1.234e-2
+3.14
+45
2.14e+2

Unless otherwise instructed sort will break ties by using the entire line of input, even when the -n option is provided and the remainder of the line is alphabetic.

$ printf "1 cat\n2 gnat\n2 mat\n1 bat\n-1 tat" | sort -n
-1 tat
1 bat
1 cat
2 gnat
2 mat

For commands that have human-readable output (e.g. du which has the -h and -si options that display numbers with SI suffixes like k, K, M, G, etc.) the -h option can be provided.

$ printf "12M\tmed.txt\n3.12K\tsmall.txt\n4.34G\tbig.txt" | sort -h
3.12K	small.txt
12M	med.txt
4.34G	big.txt

The -V option can be provided for input with a mix of alphabetical and numerical characters.

$ printf "output2\n1.2.4\noutput1.3\n0.12" | sort -V
0.12
1.2.4
output1.3
output2

The -R option can be used to display the output in random order.

$ printf "cat\ngnat\nmat\nbat\ntat" | sort -R           
mat
cat
bat
gnat
tat

$ printf "cat\ngnat\nmat\nbat\ntat" | sort -R
cat
gnat
bat
tat
mat

The -u option can be used to keep only the first copy of duplicate input lines.

$ printf "cat\ngnat\nmat\ngnat\ntat" | sort -u
cat
gnat
mat
tat

The -f option can be included with the -u option to ignore casing when determining uniqueness.

$ printf "cat\ngnat\nmat\nGnat\ntat" | sort -u
Gnat
cat
gnat
mat
tat

$ printf "cat\ngnat\nmat\nGnat\ntat" | sort -fu
cat
gnat
mat
tat

Column Sorting

The -k option can be provided to sort on specific columns instead of the entire line of input. The -k option accepts input in the form start,end (e.g. -k2,4).

# Sorted numerically by the second column
$ printf "cat\t7.1\ngnat\t1.23\nmat\t0\nGnat\t3.14\ntat\t7" | sort -k2,2n
mat	0
gnat	1.23
Gnat	3.14
tat	7
cat	7.1

3 Sorted lexicographically by the first column
$ printf "cat\t7.1\ngnat\t1.23\nmat\t0\nGnat\t3.14\ntat\t7" | sort -k1,1   
Gnat	3.14
cat	7.1
gnat	1.23
mat	0
tat	7

Note that the -k can be provided several times to create a chain of tie breaks for ordering.

# Sorted by the first column lexicographically and then the second column in reverse numerical order
$ printf "cat\t7.1\ngnat\t1.23\nmat\t0\ngnat\t0.14\ntat\t7" | sort -k1,1 -k2,2nr
cat	7.1
gnat	1.23
gnat	0.14
mat	0
tat	7

The -k optional also accepts character positions within a column for advanced sorting where the starting character is separated from the column by a . (e.g. -kstart.char,end).

# Sorted by the first column starting with the second char lexicographically and then the second column in reverse numerical order
$ printf "cat\t7.1\ngnat\t1.23\nmat\t0\ngnat\t0.14\ntat\t7" | sort -k1.2,1 -k2,2nr
cat	7.1
tat	7
mat	0
gnat	1.23
gnat	0.14

Other Options

The --debug option can be provided to help identify output that does not match expectations.

The -c and -C options can be provided to inspect input and point out the first out or order element. -c will print out the exception whereas the -C option will only affect the exit code.

$ printf "cat\ngnat\nmat\nGnat\ntat" | sort -c                        
sort: -:4: disorder: Gnat

The -o option can be provided to specify an output file for the results.