Question: While using functionality of authentication through firebase, emulator is showing error i.e.{ you attempted to use a firebase module that is not installed on your android project by calling firebase.app() }.Please help me to resolve this error.
I'm using Expo as command line input.

```
react-native version -0.63.6,
"@react-native-firebase/app": "^8.4.3",
"@react-native-firebase/auth": "^9.2.3"

```

![emulator](https://i.stack.imgur.com/GfOAc.png)

Answer: 
The variables should always be quoted:
`VAR="A-1"`

The issue in your code is with the `space in the square brackets: [...]` which you've defined in the regex: `[0-9 ]`.
There shouldn't be any space within it.

The correct code to check if some variable is starting with `A-` and ending with `digit` should be :

```
#!/bin/bash

VAR="A-1"

if [[ "$VAR" =~ ^A-.*[0-9]$ ]]; then
        echo "yes"
else
        echo "no"
fi

```

Please note the `double quotes` around the variable `VAR`.

As per the OP's comments, it looks like `sh` is being used instead `bash` , as the regex matching operator : `=~` doesn't work in `sh` and is `bash` specific.

Updated code using `sh`:

```
#!/bin/sh

VAR="A-1"

if echo "$VAR"| grep -Eq "^A-.*[0-9]$"
  then
    echo "Yes"
else
    echo "no"
fi

```
The regex to match a string which `starts with A- and ends with a digit`
should be: `^A-.*[0-9]$` or more strictly `^A-.*[[:digit:]]$`.
Then please modify your scpipt as:

```
#!/bin/bash

VAR="A-1"

if [[ $VAR =~ ^A-.*[0-9]$ ]]; then
    echo "yes"
else
    echo "no"
fi

```

Then invoke it with `bash test.sh`, not with `sh test.sh`.