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Introduction
1. Introduction to the UNIX Operating System
- 1.1. What is UNIX?
- 1.2. Types of Unix
- 1.3. The UNIX operating system
- 1.4. Files and processes
- 1.5. The Directory Structure
- 1.6. Starting an UNIX terminal
2. Tutorial One
- 2.1. Listing files and directories
- 2.2. Making Directories
- 2.3. Changing to a different Directory
- 2.4. The directories . and ..
- 2.5. Pathnames
- 2.6. More about home directories and pathnames
- 2.7. Summary
3. Tutorial Two
- 3.1. Creating files
- 3.2. Copying Files
- 3.3. Moving Files
- 3.4. Removing Files and directories
- 3.5. Displaying the contents of a file on the screen
- 3.6. Searching the contents of a file
- 3.7. Summary
4. Tutorial Three
- 4.1. Redirection
- 4.2. Redirecting the Input
- 4.3. Redirecting the Output
- 4.4. Pipes
- 4.5. Summary
5. Tutorial Four
- 5.1. Wildcards
- 5.2. Filename Conventions
- 5.3. Getting Help
- 5.4. Summary
6. Tutorial Five
- 6.1. File system security (access rights)
- 6.2. Changing access rights
- 6.3. Processes and Jobs
- 6.4. Listing suspended and background processes
- 6.5. Killing a process
- 6.6. Summary
7. Tutorial Six
- 7.1. Other useful Unix commands
- 7.2. Summary
8. Tutorial Seven
- 8.1. Compiling UNIX software packages
- 8.2. Download source code
- 8.3. Extracting source code
- 8.4. Configuring and creating the Makefile
- 8.5. Building the package
- 8.6. Running the software
- 8.7. Stripping unnecessary code
- 8.8. Summary
9. Tutorial Eight
- 9.1. UNIX variables
- 9.2. Environment variables
- 9.3. Shell variables
- 9.4. Using and setting variables
- 9.5. Setting shell variables in the .cshrc file
- 9.6. Setting the path
- 9.7. Summary
10. Tutorial Nine
- 10.1. What is *vi*?
- 10.2. Essential commands
- 10.3. Practical introduction to *vim*
11. Tutorial Ten
- 11.1. Introduction to shell script
- 11.2. Create and execute a script
- 11.3. Passing parameters to the shell
12. Annex I: basic commands
13. Annex II: First steps with Erle
14. Annex III: Network connection with Erle
- 14.1. Connecting with Erle
- 14.2. A new Erle-terminal
- 14.3. Transferring files form your computer to Erle

Erle Robotics Unix Introduction Gitbook Free

Shell Variables

An example of a shell variable is the history variable. The value of this is how many shell commands to save, allow the user to scroll back through all the commands they have previously entered. Type

echo $history

More examples of shell variables are

Variable	Meaning
cwd	your current working directory
home	the path name of your home directory
path	the directories the shell should search to find a command
prompt	the text string used to prompt for interactive commands shell your login shell

Finding out the current values of these variables.

SHELL variables are both set and displayed using the setcommand. They can be unset by using the unset command.

To show all values of these variables, type

set | less

working with erlerobot:

shel_variables

So what is the difference between PATH and path ?

In general, environment and shell variables that have the same name (apart from the case) are distinct and independent, except for possibly having the same initial values. There are, however, exceptions.

Each time the shell variables home, user and term are changed, the corresponding environment variables HOME, USER and TERM receive the same values. However, altering the environment variables has no effect on the corresponding shell variables.

PATH and path specify directories to search for commands and programs. Both variables always represent the same directory list, and altering either automatically causes the other to be changed.