if [[ ! -z "$ENV" && $ENV == 'production' ]]; then echo "production"; else echo "dev"; fi

sh: 1: [[: not found

if [ -n "$ENV" -a "$ENV" = 'production' ]

if [ "x$ENV" = 'xproduction' ]

if [ "$ENV" = 'production' ]

if [ "$var" = production ]; then
  echo PROD
fi

case $var in
  production) echo PROD;;
  "") echo EMPTY;;
  *) echo non-PROD;;
esac

if [ "${var+set}" = set ] && [ "$var" = production ]; then
  echo PROD
fi

if [ "${var-}" = production ]; then
  echo PROD
fi

awk_equal() { awk 'BEGIN{exit(!(""ARGV[1] == ""ARGV[2]))}' "$1" "$2"; }
 expr_equal() { expr "x $1" = "x $2" > /dev/null; }

 if awk_equal "$var" production; then
   echo PROD
 fi
 if expr_equal "$var" production; then
   echo PROD
 fi