topic Re: Variables in Operating System - Linux

Variables

Indrajit Bhagat — Thu, 17 Aug 2006 13:30:42 GMT

Hi Sir,
what is the purpose of variable, which are the different types of variables , how to manipulate it.

Re: Variables

James R. Ferguson — Thu, 17 Aug 2006 13:35:38 GMT

Hi:

Based upon an earlier post of yours, I believe that your question relates to the shell.

Shell variables are valid only within the shell in which they are declared. Starting a subshell or another process does not inherit a variable from the parent shell or process. That is, the variable is a 'local' one, not a 'global' one.

"Environmental" variables are 'global' variables. That is, they are visible by your current shell and any process started by it. The shell PATH, PS1, IFS, and HOME variables are examples of environmental ones.

"Shell variables" would also include the $0, $1...$n positional parameters, representing your program name and the arguments passed to it, respectively.

Shell variables include the $? which is the return value from the last command run; $# which is the number of positional parameters; and the $! which is the pid of the last background process.

Regards!

...JRF...

Re: Variables

Steven E. Protter — Thu, 17 Aug 2006 13:38:37 GMT

Shalom,

variables are changeable, hence the name containers for data.

That is as simple and basic as I can put it.

env dipslays all set variables and that may help you understand what they are for.

SEP

Re: Variables

A. Clay Stephenson — Thu, 17 Aug 2006 13:40:03 GMT

Your question is all but meaningless without context. In general, a variable is by definition something that can be changed as opposed to a constant which is fixed.

It would help if you would narrow trhe scope of your question. Is is mathematical? Does it pertain to shell scripting? Perl? C? FORTRAN? Computer languages in general?

One very basic difference between computer languages and matmematics is that:

X = X + 1

is a perfectly valid computer statement but absolute nonsense in algebra. That is why without a scope, your question is all but impossible to answer.

Re: Variables

Torsten. — Thu, 17 Aug 2006 13:46:33 GMT

basic explanation (like the question):

http://en.wikipedia.org/wiki/Variable