Count unique values in a bash array

Question

I have an array ${sorted[@]}. How can I count the frequency of occurrence of the elements of the array.

e.g:

Array values:

bob
jane
bob
peter

Results:

bob 2
jane 1
peter 1

Socowi · Accepted Answer · 2018-03-14 08:53:04Z

6

(IFS=$'\n'; sort <<< "${array[*]}") | uniq -c

Counting occurrences of unique lines is done with the idiom sort file | uniq -c.
Instead of using a file, we can also feed strings from the command line to sort using the here string operator <<<.
Lastly, we have to convert the array entries to lines inside a single string. With ${array[*]} the array is expanded to one single string where the array elements are separated by $IFS.
With IFS=$'\n' we set the $IFS variable to the newline character for this command exclusively. The $'...' is called ANSI-C Quoting and allows us to express the newline character as \n.
The subshell (...) is there to keep the change of $IFS local. After the command $IFS will have the same value as before.

array=(fire air fire earth water air air)
(IFS=$'\n'; sort <<< "${array[*]}") | uniq -c

prints

      3 air
      1 earth
      2 fire
      1 water

answered Mar 13, 2018 at 19:26

Socowi

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1 Comment

@user9487425 The old answer worked on bash 3.2 but not on bash 4.3 (wouldn't have expected that). I updated the answer to work on both versions.