extracting a variable's value from text file using bash

Question

I am using Linux and bash. I have a simple text file like below:

VAR1=100
VAR2=5
VAR3=0
VAR4=99

I want to extract by means of bash the value of VAR2, that is 5.

How could I do that?

Answer 1

Assuming the file is called vars.txt

sed -n 's/^VAR2=\(.*\)/\1/p' < vars.txt

You can use the value elsewhere like this using single back quotes

echo VAR2=`sed -n 's/^VAR2=\(.*\)/\1/p' < txt`

Answer 2

The simplest way might be to use source or simply . to read and execute the file. This would work with your example, because there are no spaces in the variable values. Otherwise you need to use grep + cut or awk, as stated in other answers.

. /path/to/your/file
echo $VAR2

[edit] As stated by dawg, this would make the other variables available in your script too, and possibly overwrite existing variables.