how bash shell script construct array element with space [duplicate]

Question

I want to construct array element with space, it works while run in command line:

pc:/tmp$ b=('1 2' '3 4')
pc:/tmp$ echo $b
1 2
pc:/tmp$ echo ${b[1]}
3 4

But it get the elements split with space in script:

pc:/tmp$ cat t.sh
a="'1 2' '3 4'"
echo $a
b=($a)
echo $b
echo ${b[1]}
echo ${b[2]}

pc:/tmp$ bash t.sh
'1 2' '3 4'
'1
2'
'3

I want to get '1 2' with echo $b as get '3 4' with ${b[1]} in script.

How could I achieve this?

And why it can't not works in script but works in command line?

b=($a) splits the string on white space. You would have to write a parser for your a to tear it apart. — user1934428
– user1934428, Commented Sep 27, 2021 at 14:19
If you tested b=($a) at the command line it would behave just the same way as it did in your script. This isn't a script-vs-command-line difference. — Charles Duffy
– Charles Duffy, Commented Sep 27, 2021 at 15:32
BTW, among the answers on the duplicates, I strongly suggest finding one that uses either the Python shlex module (if you want the closest possible accuracy to a real POSIX sh parser), or xargs printf '%s\0' (if you want something that's available everywhere and doesn't add more bugs than the minimum set xargs forces). — Charles Duffy
– Charles Duffy, Commented Sep 27, 2021 at 15:35
@CharlesDuffy THX, thanks for your time, maybe I should improve my search skill, that all relevant questions are helpful. — Victor Lee
– Victor Lee, Commented Sep 27, 2021 at 16:18

Paul Hodges · Accepted Answer · 2021-09-27 15:27:07Z

4

The code a="'1 2' '3 4'" does not create an array, it creates a string with embedded single-quotes.

$: a="'1 2' '3 4'"
$: echo "[$a]"
['1 2' '3 4']

If you want to create an array, you have to use the right syntax.

$: a=( '1 2' '3 4' )
$: printf "[%s]\n" "${a[@]}"
[1 2]
[3 4]

Then if you want to copy it to another array, just treat it like an array instead of a string.

b=( "${a[@]}" )
printf "[%s]\n" "${b[@]}"
[1 2]
[3 4]

To convert the string created in a="'1 2' '3 4'" to an array is a little trickier.

IF you know that the format is a consistent match for the above, try this:

$: echo "[$a]"
['1 2' '3 4']
$: IFS='#' read -ra b < <( sed -E "s/' +'/#/g; s/ *' *//g" <<< "$a" )
$: printf "[%s]\n" "${b[@]}"
[1 2]
[3 4]

but generally, this is a bad plan. Try to fix your input!

answered Sep 27, 2021 at 14:40

Paul Hodges

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4 Comments

I means I have a string variable a="'1 2' '3 4'", and how could I translate it to a array? THX.

That's a little harder. How consistent is that format?

We already have existing knowledge base entries that do what the OP is asking for.

@PaulHodges THX, the pattern is consistent with mine, it can solve my problem, THX.