问题:

I would like to expand a variable in Bash. Here's my example:

variable="{1,2,3}"
echo $variable

Expected output:

1 2 3

Actual output:

{1,2,3}

回答1:

The expansion doesn't work because of the order in which bash performs command-line expansion. If you read the man page you'll see the order is:

Parameter expansion happens after brace expansion, which means you can't put brace expansions inside variables like you're trying.

But never fear, there's an answer! To store a list of numbers in a variable, you can use an array.

variable=(1 2 3)
echo "${variable[@]}"

This won't work first because double-quotes suppress brace expansion:

variable="{1,2,3}"

This still won't work because bash will not assign a list to a variable:

variable={1,2,3}

The solution is to assign your list to an array:

$ variable=( {1,2,3} )
$ echo "${variable[@]}"
1 2 3