I want to assign the output of a mongo command (i.e database names) to a bash array variable but I am not sure how to go about it.

I am getting an error :

dump.sh
Starting-BACKUP
dump.sh
./dump.sh: line 16: declare: `–a': not a valid identifier
./dump.sh: line 24: mongo: command not found   
Database backup was successful

when I attempt using dump.sh below:

#!/bin/bash
declare –a databases=()
    databases=$(mongo --quiet --uri="mongodb://root:mypassword@mongodb-prom/admin" --authenticationDatabase admin --eval="show dbs;" |  cut -d " " --field 1)
    echo $databases

Ordinarily I am able to get a listing of the databases when I kubectl into the pod with following steps :

$ kubectl exec -it mongodb-prom-xxxxxxxxx-dddx4 -- sh
$ mongo
> use admin
> db.auth('root','mypassword')
> show dbs
admin      0.000GB
platforms  0.000GB
users      0.000GB

I am not sure why the mongo command is not being recognized because the same script is able to execute the mongodump command below :

mongodump --uri="<uri_here>" --authenticationDatabase admin --gzip --archive=/tmp/"<variable_here>".gz

UPDATE : This is the associated Dockerfile. My expectation is that both mongo and mongodump should be working by default in a mongo container but it seems only mongodump is working for now

FROM mongo
WORKDIR /opt/backup/
WORKDIR /usr/src/configs
COPY dump.sh .
RUN chmod  x dump.sh

My two issues :

1. Is my syntax correct for the variable assignment (I suspect its not correct) ?
2. How should I properly declare the array variable to avoid the warnings ?

NB : Mongo tooling is already installed on the container and is actually working for mongodump

CodePudding user response：

You don't need declare -a. Simply putting the value inside () in the assignment will make it an array.

To get all the elements of an array, you have to use ${variable[@]}. $variable is equivalent to ${variable[0]} and just retrieves the first element.

databases=($(mongo --quiet --uri="mongodb://root:mypassword@mongodb-prom/admin" --authenticationDatabase admin --eval="show dbs;" |  cut -d " " --field 1))
echo "${databases[@]}"

CodePudding user response：

With bashv4 , mapfile is available, with Process Substitution.

mapfile -t databases < <(mongo --quiet --uri="mongodb://root:mypassword@mongodb-prom/admin" --authenticationDatabase admin --eval="show dbs;" |  cut -d " " --field 1)

Now check the value of the databases array

declare -p databases

Your code has

declare -a databases=()

but

databases=$(...)

is not an array, the $(...) construct is Command Substitution.

See also Bash Arrays