Execute Input - Shell Scipt

I am making a shell script in linux with the bash shell. I am wondering what I can do to execute the input of a user. I am trying to get the user to enter an environment variable that already exists. Then my script will execute the variable they entered.
[code]echo "enter envir variable:"
read Envir
echo $Envir
[code/]

When I run the program and enter an environment var like "$PATH" it just echoes "$PATH" how do I get it to execute the value of $PATH, which should be:
"bash: /usr/bin:/bin:/usr/local/bin:/usr/X11R6/bin:/usr/local/jdk/bin:/usr/local/ oracle/software/bin:"

Like this?

Code:

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$ a="echo hello"
$ eval $a
hello

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so its called an eval command, i'm new to this. thanks