reading variable in unix shell script and performing operation

Question

I need to read a variable in shell script and using that variable to perform some operation. For e.g. I am reading variable markets from config and using this variable to find out the value of another variable redis_host_silver_$j

command used :-

for j in `echo $markets | awk -F"," '{ for(i=1; i<=NF; ++i) print $i }'`;
do
    echo $(redis_host_silver_$j);
done

Can anyone help me in this?

im getting error like below :- + for j in 'echo $markets | awk -F"," '\''{ for(i=1; i<=NF; ++i) print $i }'\''' ++ redis_host_silver_uk test.sh: line 61: redis_host_silver_uk: command not found — Vishal Patial
– Vishal Patial, Commented Feb 17, 2017 at 8:24
Try quoting around your echo, like echo "redis_host_silver_$j"; — Jack
– Jack, Commented Feb 17, 2017 at 8:29
Also if you have the permissions to do so, it would be helpful to edit the original question to add error message — Jack
– Jack, Commented Feb 17, 2017 at 8:30
eval might be needed... You probably want arrays though... Also $(stuff) will run stuff and replace in the result. (a=1;$(stuff_$a) will run stuff_1) — Gert van den Berg
– Gert van den Berg, Commented Feb 17, 2017 at 14:07

Jack · Accepted Answer · 2017-02-17 08:49:25Z

1

The error is in the echo $(redis_host_silver_$j); part.

The $() syntax in bash expands what's inside as a command so you're actually trying to execute redis_host_silver_$j

Try:

for j in `echo $markets | awk -F"," '{ for(i=1; i<=NF; ++i) print $i }'`;
do
    echo "redis_host_silver_$j";
done

If redis_host_silver_... is a name of a variable that you want the value of then do this:

for j in `echo $markets | awk -F"," '{ for(i=1; i<=NF; ++i) print $i }'`;
do
    VAR=redis_host_silver_$j; echo ${!VAR};
done

Note the curly brackets

edited Feb 17, 2017 at 8:49

answered Feb 17, 2017 at 8:35

Jack

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2 Comments

Jack Over a year ago

Glad to help. Which method did you use?

Gert van den Berg Over a year ago

Indirect expansion seems like a much better option than eval... (Which is how I would have approached it...)

grail · Accepted Answer · 2017-02-17 16:43:03Z

0

I personally would steer away from using a for loop to read data directly from process substitution which may or may not have white spaces in it. And whilst the indirect call may work, I would say that your variable type is wrong and the second variable, redis_host_silver, should actually be an array with the items from the file as indices.

So maybe something like:

IFS="," read -ra items <<<"$markets"

for item in "${items[@]}"
do
    echo "${redis_host_silver[$item]}"
done

If the values from "markets" are numbers, then "item" variable in call to array does not require "$"

answered Feb 17, 2017 at 16:43

grail

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