In bash script, can we set variable values using command line argument

Question

I am looking to modify bash script to set variable by either command line argument or from user input (read command). if argument passed as command line, script should be executed without asking for user input.

I am able to set variable either command line argument or user input but not both way in same script

#!/bin/sh

ENVIRONMENT_NAME=$1
EMAIL=$2

read ENVIRONMENT_NAME
read EMAIL

echo "$ENVIRONMENT_NAME"
echo "$EMAIL" 

if I execute like below read command should take values from $1 and $2.

./<scriptname> <environment_name> <email>

Answer 1

To check whether an argument is provided, you would look at the value of $# (the number of arguments):

#! /bin/sh -

if [ "$#" -ge 1 ]; then
  ENVIRONMENT_NAME=$1
else
  IFS= read -r ENVIRONMENT_NAME || exit # on EOF
fi

if [ "$#" -ge 2 ]; then
  EMAIL=$2
else
  IFS= read -r EMAIL || exit # on EOF
fi

Answer 2

Well. You have to add a check whether positional vars are set or not. If not, then ask for use input.

Something like this:

#!/bin/sh

[ -n "$1" ] && ENVIRONMENT_NAME=$1 || { echo -n "Enter environment name: "; read ENVIRONMENT_NAME; }
if [ -n "$2" ]; then
        EMAIL=$2
else
        echo -n "Enter email: "
        read EMAIL
fi


echo "env=$ENVIRONMENT_NAME"
echo "email=$EMAIL"

Note that I used different constructions for conditional check, just to show that there are different ways and you might pick the one which is more convenient for you.

Also note, that the one with || && should be used more careful, as it might fall to || ... even in case something goes wrong in the part between && .. ||.