What are the special dollar sign shell variables?

Question

In Bash, there appear to be several variables which hold special, consistently-meaning values. For instance,

./myprogram &; echo $!

wil

Answer 1

Take care with some of the examples; $0 may include some leading path as well as the name of the program. Eg save this two line script as ./mytry.sh and the execute it.

#!/bin/bash

echo "parameter 0 --> $0" ; exit 0

Output:

parameter 0 --> ./mytry.sh

This is on a current (year 2016) version of Bash, via Slackware 14.2