collection of common scripting problems and its solutions for both unix bash and windows cmd (batch) platforms

bash and win scripts.md

if file not exists

bash:

if [ ! -f .env ]; then
    echo "ERR: .env file not found. Please create one, details: https://devcenter.heroku.com/articles/heroku-local#set-up-your-local-environment-variables"
    exit 1
fi

win:

if not exist .env (
    echo ERR: .env file not found. Please create one, details: https://devcenter.heroku.com/articles/heroku-local#set-up-your-local-environment-variables
    exit /B 1
)

set default value to var (if it's unset)

bash:

AWS_REGION=${AWS_REGION:=us-east-1}
AWS_PROFILE=${AWS_PROFILE:=nonprod}

exit if var is empty

bash:

MONGODB_URI=${MONGODB_URI:?"ERR: required var is empty"}
ARG_1=${1:?"ERR: first argument must be defined"}

win:

if [%MONGODB_URI%] == [] (
    echo MONGODB_URI: ERR: required var is empty
    exit /B 1
)

get dir's absolute path by relative (dir must exists)

bash:

SOURCE=relative/path/to/dir
SOURCE=$(cd $SOURCE && pwd)

set vars defined in separate file

Given variables defined in the .env file like:

MONGODB_URI=mongodb://user:pass@host:port/db
FOO=BAR

We can assign (evaluate) those vars and use them as a standard script vars

bash:

source .env
echo ${MONGODB_URI}

win:

for /F "tokens=*" %%A in (.env) do SET %%A
echo %MONGODB_URI%