For accessing the environment variable in a readable way, I'd make a shell function of it:

getenv() { 
    awk 'BEGIN {print ENVIRON[ARGV[1]]}' "$1";
}

You can then use it as

$ getenv agent1.ip
192.168.100.137
$ myvar=$(getenv agent1.ip)
$ echo "$myvar"
192.168.100.137

Differences with the accepted answer are:

• robustness: supports also newlines in the variable value (grep and cut work on lines)
• efficiency: only one fork (awk) instead of 3 (env, grep, cut) in a pipeline (which also has to set up i/o buffers)

There is also another question about Exporting a variable with dot (.) in it.
Short answer: you can't, but you needn't, except for calling another executable. In that case use env.