Add a conditional SORT variable to mongoexport

Question

I'm trying to set up a conditional --sort option in mongoexport but I'm having trouble with the string interpretation of my variable. Here is the code I'm trying to run :

#!/bin/bash
if [[ $IS_PROD == "true" ]]
then
   SORT='--sort "{_id : -1}"'
else
   SORT=""
fi

$MONGODB_HOME/bin/mongoexport \
--host=$HOST \
--port=$PORT \
--username=$USER \
--password=$PWD \
--db=$DB \
--limit=$LIMIT \
$SORT \
--collection=my_collection  | \
sed 's,\\,\\\\,g' \
> $TMP_FILE

While running this I get the following error error parsing command line options: invalid argument for flag '--sort' (expected string): invalid syntax

I've tried several quotes configuration and still couldn't make it work. Could someone please help me on this one?

Thanks

Answer 1

using bash array

#!/bin/bash
if [[ $IS_PROD == "true" ]]
then
    SORT=(--sort "{_id : -1}")
else
    SORT=()
fi

$MONGODB_HOME/bin/mongoexport \
--host=$HOST \
--port=$PORT \
--username=$USER \
--password=$PWD \
--db=$DB \
--limit=$LIMIT \
"${SORT[@]}" \
--collection=my_collection  | \
sed 's,\\,\\\\,g' \
> $TMP_FILE

Explanation: using single quotes prevent shell expansions and double quotes are literal, but after variable expansion the double quotes are still litteral and expanded string is split by spaces.

Otherwise to work around unbound variable bug

#!/bin/bash

options=(--host=$HOST \
--port=$PORT \
--username=$USER \
--password=$PWD \
--db=$DB \
--limit=$LIMIT)
if [[ $IS_PROD == "true" ]]
then
    options+=(--sort "{_id : -1}")
fi

$MONGODB_HOME/bin/mongoexport \    
"${options[@]}" \
--collection=my_collection  | \
sed 's,\\,\\\\,g' \
> $TMP_FILE