Dealing with variables in shell environment - canonical way

One of the very important elements of interactive work with UNIX/Linux is a shell, especially variables in shell environment. To work with variables sometime can be easy, sometime hard. So here I will try to show some of the ideas how to deal with them.

1. how to see the variable: use one of the commands:

set|grep VAR
or

echo $VAR

2. how to set variable:

VAR=value;export VAR

or if you want to add some value to the existing in the variable

VAR=$VAR:value;export VAR

Of course export is need only in case you want to populate value to subinstrances of current shell. I use this way because it work on bourne shell, korn shell and bash. If you are sure script will work only in bash and/or korn shell use short form:

export VAR=value

3. how to destroy the variable:

unset VAR

I can use

VAR="";export VAR

but this only will "zero" the content and not destroy the variable

4. how to change (inside) the content of variable. You can make it entering the entire string (or number), but this little script will help you do it on the fly. Do not forget script is just an example and you should "tune" it to do the real work

VAR=`echo $VAR|sed s/string//g`;export VAR