Using variable as a key in an bash associative array

Question

I'm trying to read the English dictionary in Linux into an associative array, using the words as keys and and predefined string as a value. This way I can look up words by key to see if they exist. Also I need all to words to be lowercase. It's fairly simple but the bash syntax is getting in my way. When I run the code below, I get a 'bad array subscript' error. Any thoughts as to why that might be ?

 function createArrayFromEnglishDictionary(){
        IFS=$'\n'
        while read -d $'\n' line; do
            #Read string into variable and put into lowercase.
            index=`echo ${line,,}`
            englishDictionaryArray[$index]="exists"
            done < /usr/share/dict/words
            IFS=$' \t\n'
    }

What is the syntax ${VAR,,}? I've never seen this before, and can't find any references elsewhere — Zoey Hewll
– Zoey Hewll, Commented Oct 4, 2017 at 8:00

Jobin · Accepted Answer · 2015-09-16 10:28:15Z

7

I think following example will help..

$ declare -A colour
$ colour[elephant]="black"
$ echo ${colour[elephant]}
black

$ index=elephant
$ echo ${colour["$index"]}
black

answered Sep 16, 2015 at 10:28

Jobin

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Comments

ribbons · Accepted Answer · 2018-12-29 19:04:15Z

5

$index is empty at some point. You also have a rather totally pointless use of echo assuming you wanted the line verbatim and not whitespace compressed. Just use index="${line,,}".

edited Dec 29, 2018 at 19:04

ribbons

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answered Mar 18, 2012 at 21:07

jørgensen

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3 Comments

Asgeir Over a year ago

index="${line,,}" didn't work, but I don't know why. I had tried this before and expected it to work. Should the key-value assignment be any different from what it is like now ?

Asgeir Over a year ago

It seems to work now, I changed englishDictionaryArray[$index]="exists" to englishDictionaryArray["${index}"]="exists" at first, that didn't work. And of course, the error was completely unintuitive, I had to add spaces at both sides of ". so [ "${index}" ] works. Man I hate bash sometimes.

jørgensen Over a year ago

So don't use bash for these things. There are many other, more suitable scripting languages for this kind of advanced string juggling-and-manipulation.

glenn jackman · Accepted Answer · 2012-03-19 00:50:55Z

2

To use associative arrays in bash, you need bash version 4, and you need to declare the array as an associative array with declare -A englishDictionaryArray

http://www.linuxjournal.com/content/bash-associative-arrays

answered Mar 19, 2012 at 0:50

glenn jackman

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Comments

philcolbourn · Accepted Answer · 2013-01-02 02:12:43Z

1

Combining your work and other answers, try this:

I'm using GNU bash, version 4.2.37(1)-release (x86_64-pc-linux-gnu)

#!/bin/bash
declare -A DICT
function createDict(){
    while read LINE; do
        INDEX=${LINE,,}
        DICT[$INDEX]="exists"
    done < /usr/share/dict/words
}

createDict

echo ${DICT[hello]}
echo ${DICT[acdfg]}
echo ${DICT["a's"]}

answered Jan 2, 2013 at 2:12

philcolbourn

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3 Comments

philcolbourn Over a year ago

@Daniel Kuta, 6 years later and it still seems to work for me. This does not help you, but perhaps you can provide error messages and output and version of bash?

fornwall Over a year ago

Note that /bin/bash on macOS is bash version 3.2, which does not support associative arrays. Mac users could install and use latest bash from e.g. homebrew.

Yzmir Ramirez Over a year ago

For those who don't know ${LINE,,} will return a lowercase version of $LINE

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