Reading a space-delimited string into an array in Bash

Question

I have a variable which contains a space-delimited string:

line="1 1.50 string"

I want to split that string with space as a delimiter and store the result in an array, so that the following:

echo ${arr[0]}
echo ${arr[1]}
echo ${arr[2]}

outputs

1
1.50
string

Somewhere I found a solution which doesn't work:

arr=$(echo ${line})

If I run the echo statements above after this, I get:

1 1.50 string
[empty line]
[empty line]

I also tried

IFS=" "
arr=$(echo ${line})

with the same result. Can someone help, please?

Solution 1

In order to convert a string into an array, create an array from the string, letting the string get split naturally according to the IFS (Internal Field Separator) variable, which is the space char by default:

arr=($line)

or pass the string to the stdin of the read command using the herestring (<<<) operator:

read -a arr <<< "$line"

For the first example, it is crucial not to use quotes around $line since that is what allows the string to get split into multiple elements.

See also: https://github.com/koalaman/shellcheck/wiki/SC2206

Solution 2

In: arr=( $line ). The "split" comes associated with "glob".
Wildcards (*,? and []) will be expanded to matching filenames.

The correct solution is only slightly more complex:

IFS=' ' read -a arr <<< "$line"

No globbing problem; the split character is set in $IFS, variables quoted.

Solution 3

Try this:

arr=(`echo ${line}`);

Solution 4

If you need parameter expansion, then try:

eval "arr=($line)"

For example, take the following code.

line='a b "c d" "*" *'
eval "arr=($line)"
for s in "${arr[@]}"; do 
    echo "$s"
done

If the current directory contained the files a.txt, b.txt and c.txt, then executing the code would produce the following output.

a
b
c d
*
a.txt
b.txt
c.txt

View more solutions

Comments

[codeforester]

See this answer on Unix & Linux Stack Exchange: Using sed with herestring (<<<) and read -a. set -f; arr=($string); set +f seems to be faster than read -r -a <<< $string.

[Gabriel Staples]

Related: how to convert a newline-delimited string to a bash array: Convert multiline string to array

[Gabriel Staples]

See also these demonstrations and examples here: shellcheck SC2206: Quote to prevent word splitting/globbing, or split robustly with mapfile or read -a.

[Banjer]

and to do a sanity check of your beautiful new array: for i in ${arr[@]}; do echo $i; done

[Banjer]

or just echo ${arr[@]}

[Keith Hughitt]

Nice -- This solution also works in Z shell where some of the other approaches above fail.

[Tino]

Both ways may fail if $line has globbing characters in it. mkdir x && cd x && touch A B C && line="*" arr=($line); echo ${#arr[@]} gives 3

[Zorf]

The looping is wrong, it splits the array fine and the pipe into tr is superfluous but it should loop over "${arr[@]}" instead, not $arr

[Dave]

declare -a "arr=($line)" will ignore IFS delimiters inside quoted strings

[georg]

Both solutions work for me on the cmd-line. arr=($line) doesn't work for me within a bash script whereas read -a arr <<<$line does.

[Awknewbie]

What need to be done if the file was delimited eg :"1,1.50,string" . Can delimite be specified before feeding to array.

[kev]

@Awknewbie try this command: arr=($(echo '1,1.50,string' | tr ',' ' '))

[vr3C]

Its does the work, could you please explain why it works?

[Manuel Rozier]

Works also with ksh. Beware that declaring arr=("a b") won't work, you need to explicitly declare the intermediary variable "line". line="a b" then arr=($line)

[Tim Bird]

You can avoid wildcard expansion with: set -f && arr=($line) && set +f

[Johnny Wong]

@Tino No. When line='*', read -a arr <<<$line always work, but only arr=($line) fails.

[Tino]

@JohnnyWong Good find! Sorry that I mixed that with ksh where a='*'; read -A b <<<$a fails while a='*'; read -A b <<<"$a" works. Note that bash uses read -a while ksh uses read -A.

[Johnny Wong]

Remark: this doesn't work either when the line have '*' in it, like line='*'

[codeforester]

This should be the accepted answer. The statement arr=($line) in the accepted answer suffers from globbing issues. For example, try: line="twinkling *"; arr=($line); declare -p arr.

[codeforester]

Quoting is optional for herestring, <<< but it may be a good idea to still use double quotes for consistency and readability.

[artu-hnrq]

Looking for a GNU Make 4.2.1 solution, but is not that

[artu-hnrq]

Looking for a GNU Make 4.2.1 solution, but it doesn't did the job

[done]

@artu-hnrq Make use the sh shell. That shell has no arrays. The question is about arrays. Can't give you an answer compatible with both requirements. Unless you claim that the positional arguments are the only array in sh and, then, this: set -- $line; printf '%s\n' "$@" would work. Note that glob characters are still a problem in this case.

[artu-hnrq]

You are right @Isaac! I made my own question

[TonyH]

Shellcheck SC2207 argues against arr=($line). I like how concise this is, but maybe it's not worth using?

[elulcao]

This solution worked for me, thanks a lot.

[Gabriel Staples]

See also: shellcheck SC2206: Quote to prevent word splitting/globbing, or split robustly with mapfile or read -a.

[Togomi]

Very simple solution for CentOS8