Prompting for input in bash script and then using it in the script

Question

OS: Ubuntu 14.04

I am new to shell programming (and I don't have time to become an expert, as this is something I do not envision doing in regular basis), but I need to do some stuff in scripts to prep for Rails app deployments. I have the following script:

#!/bin/bash
cd ~
sudo ls -l
read -p $'Enter version of Ruby you want to use, ex: 2.1.7\n' rubyv
if [ "$rubyv" = '' ]; then
  echo 'You did not enter a Ruby version to use, exiting...'
  exit
fi
echo '    You entered '$rubyv
read -rsp $'If this not what you wanted press any key to exit, otherwise, press c to continue\n' -n1 key
if [ "$key" != 'c' ]; then
  exit
fi

Then I would like to continue the script by using $rubyv to install Ruby using rvm, something like:

rvm install "$rubyv"

For a test, I tried entering a directory name that I created, and then added this to the end of the script:

cd "$rubyv"

But nothing is happening. What am I missing?

Solution:

It appears as the cd command is executing fine, but the reason I do not see it, is that when the script exists, I am returned to ~, the directory I started from. I verified that I was in the directory that I cd to, by doing an ls -l at the end of the script, and it did give me the proper listing

Answer 1

Each shell script runs in its own environment. It means that the variable $rubyv exists only inside the script.

Directory change can be done only inside the script. Once that script starts it changes directory in its environment to your HOME by cd ~. So, all commands inside the script are executed from HOME, for example ls -l (by the way it is strange to execute ls with sudo in your home directory).

After script termination the variable $rubyv is not valid and you are back in the directory where the script was executed.

---

It is also possible to excute script in the current shell without creation of subshell using dot space dot slash:

. ./scriptname

In that case all commands will be executed directly in the current shell, so it will affect the current environment and directory. However, it is better to run helper scripts in usual way (just by ./scriptname) to protect the current environment).