Currently I have a curl command that I want to store in a local variable. I know I could use `` or $() to get it done, but a variable inside the command stops me from doing so.
local sample_mapping="$(curl -XGET '${search_host}/${index}/_mapping')"
where search_host and index are two variables previously set. This command fails because Couldn't resolve host '$search_host'
The other posts didn't talk about what to do when dealing with variables. Anyone has any idea?
This is the command in your command substitution:
curl -XGET '${search_host}/${index}/_mapping'
This command will not work on its own. The problem that you are observing is due to the single quotes, not to the use of command substitution, $(...).
Inside single-quotes, variables are not expanded. Since you need variable expansion, use double-quotes:
curl -XGET "${search_host}/${index}/_mapping"
Putting the above in your original command:
local sample_mapping="$(curl -XGET "${search_host}/${index}/_mapping")"
Note that quotes and command substitutions can nest : the fact that there are double quotes inside the command substitution has no effect on the double quotes outside of the command substitution.
Let's define some variables:
$ search_host=http://google.com
$ index=index.html
Now, let's try the command with single-quotes:
$ a=$(curl -XGET '$search_host/$index')
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0curl: (6) Could not resolve host: $search_host
The above failed with an error message similar to the one you observed: Could not resolve host: $search_host
Let's try again with double-quotes:
$ a=$(curl -XGET "$search_host/$index")
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 229 100
229 0 0 520 0 --:--:-- --:--:-- --:--:-- 521
The above succeeded.
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