What is a Shell?
 

Comming from the MSFT world, Im used to being able to run executables from the command line if I am in the directory where the app is located....or if my path is setup correctly.

I recently discovered situations where I cant run apps in linux even when I am cd..'d into the same relative path or location.

I am told that the "shell" is different than dos. I already know that, but would like a clear rundown on how linux/unix treats paths for root, or users...or users with the su - applied. Is there a howto about this? Does is matter what kind of shell Im in? What properties do different shells have?

A shell is a program that takes user input and passes it to the system.

As far as I know ALL shells use the $PATH environment variable to determine where to look for programs.

You can find your $PATH with the following syntax (I'll assume bash for all examples):

On my system this gives me:

The shell will look only in those directories for programs, you can set it to look for programs with whatever the current working directory is by adding "." to the $PATH. However I wouldn't bother, the programs you run regulary should be in the bin directories, when you want to run a program that isn't in your $PATH you can provide a path to it.

For example, to run "foo" in the currect directory:

The most popular shell nowadays is bash, and it's also the default in many Linux distributions. For more info on bash, see the following:

http://www.tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html
http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/index.html

I actually have submitted this as a term in our LQ glossary under shell in the S section of course, take a look here: http://www.linuxquestions.org/questions/glossary.php

I gotta say - thanks for this forum, ive been fumbling around for a month now, and one day here has helped me hugely!

about bin/bash and bin/sh when i created a user today it defaulted to bin/sh this user has a virtual server and will only be given ftp access to a restricted directory - (via chroot next question) should I alter their shell to bin/bash? -

it depends on what the user may really prefer. either will work, but bash is usually the default and plus it has more features/functions which in most cases makes it easier to work with.

users who are for ftp access _only_ should not have a shell at all.

users without a shell will be able to access services on the box but will not be able to login through ssh or telnet.