The shell is an interpreter (a program) that lets you interact with the operating system
- The shell is a command-line interpreter that lets you interact with Linux
- The shell takes what you type and "decides" what to do with it
- The shell is actually a scripting language somewhat like Python
- It is always possible to change shell (either temporarily or permanently)
You can type a program name at the terminal prompt and then type [Return]
- Change default bg color
- Change text size, colour and font
- Increase/decrease transparency
- Resize it
- Have multiple windows open side by side
- Have multiple "tabs" open at the same time
- Change the command prompt (most commonly a $ or % sign)
- Make the cursor blinking
allows you:
- to send typed instructions to the computer (i.e., run programs, move/view files, etc.)
- to see the output that results from those instructions.
Every time you type any Unix command and press enter, the computer will attempt to follow your instructions and then, when finished, return you to the command prompt.
Type the Unix command ls at the command prompt: what happens?
The file-system is arranged in a hierarchical structure, like an inverted tree
The top of the hierarchy is traditionally called root
When you first login, the current working directory is your home directory (containing files and directories that only you can modify)
Challenge #1
What do you need to navigate the filesystem?
Make a list of the actions needed to navigate
(example: change directory)
See the Solution to challenge #1
Slashes separate parts of the directory path:
/home/allegra/Documents/Training/materials/Unix/Academis_Linux.pdf
Challenge #2
What do you need to be able to do/manage stuff in the filesystem? (example: Make a new directory) Write a list of actions Tip Think of what you need in, e.g., Windows or Mac OSX
See the Solution to challenge #2
Before talking about Linux commands, we need to answer a question:
What is a computer program?
Which ones do you know?
- A text file
- Word
- OS
- The shell
- An Excel data file
- A database
- Power point
- The Linux Terminal
- A Linux command
- About Unix commands
- Commands are themselves programs
An example of command:
%rm myfile.txt [Return]
- The shell searches the file containing the program
rm - executes the program
rmonmyfile.txt - After the process
rm myfile.txthas finished running, the shell returns the prompt%to you, indicating that it is waiting for further commands.
command_name -options <file> [Return]
%ls [Return]
%ls –l [Return]
%ls -l <dirname> [Return]
%ls -ltr <dirname> [Return]
man <command name> [Return]
whatis <command name> [Return]
OPTIONS and ARGUMENTS Replace the XXX
There are commands that can take XXX
Commands may also take XXX
XXX change the behaviour of the command
XXX are the objects on which commands act
You will specify XXX using a XXX
The command name, XXX and XXX must be separated by XXX
If you've made a typo: Ctrl-XXX to cancel the whole line
Unix is XXX-sensitive
Ctrl-XXX sets the cursor at the beginning of the line
Ctrl-XXX sets the cursor at the end of the line
You can use up and down XXX to recall commands
You can use the XXX to complete a command or file name
The command XXX tells you where is a given program
You can use a XXX to write programs
-
A process is an executing program identified by a unique PID (PID = Process IDentifier)
-
A file is a collection of data
- Access your home directory using the command-line interface
- Start the nano text editor
- Create a text file
my_first_shell_script.sh
-
Write the commands in a file, save and exit
-
Go to the command-line interface and type
lsat the prompt
Is my script executable?
Each file (and directory) has associated access rights, which may
be found by typing ls -l
Access rights on directories
- r allows users to list files in the directory
- w allows users to delete files from the directory or move files into it
- x allow users to access files in the directory
How can I make my script executable?
Changing access rights: chmod
%chmod go-rwx myfile.txt
%chmod a+x my_script
| Symbol | Meaning |
|---|---|
| u | user |
| g | group |
| o | other |
| a | all |
| r | read |
| w | write (and delete) |
| x | execute (and access direcotry) |
| + | add permission |
| - | take away permission |
3. You have to tell the shell which "interpreter" will read and execute the program AND where it will find it You have to tell the shell which "interpreter" will read and execute the program AND where it will find it
"Aha, you want to use the program located at /bin/bash to interpret all the instructions that follow" (Bradnam&Korf - Unix and Perl to the Rescue)
want to run OR….
In other words, if you want to execute the script you have to tell Linux where it can find it
Where Linux searches for programs?
Either you explicitly tell Linux where it can find your script…
- by prefixing its name with a path:
~allegra/Documents/shell_commands.sh - If you are in the same directory as the one of the program, you can type:
./shell_commands.sh
Or you can specify the script's path in the PATH environment variable
- If you simply type (at the prompt):
shell_commands.sh
Linux will look up a list of predefined directories to see if that program exists in any of those locations
If it finds a match, it will try to run the program and stop searching in any other directory
If it cannot find a match, it will print "command not found"
You may think of the PATH variable as a sort of address book UNIX environment variables
Linux keeps track of several special variables that are associated with your account
- Written in upper-case letters
- Use echo and prefix the variable with a $ if you want to get the content
Try the following commands:
- printenv
- echo $SHELL
- printenv SHELL
- echo $PATH
- echo PATH
- echo $USER
If the system returns a message saying
"command: Command not found"
this indicates that either the command doesn't exist at all on the system or it is simply not in your path.
- Any program in
~/allegra/my_scriptscan be run from anywhere in the filesystem (as long as the program file is executable) - You can use tab-completion
- Your scripts will be treated like any Linux command
For shells in the bash family:
export PATH=$PATH:~/allegra/my_scripts
For shells in the csh family:
setenv PATH $PATH\:~/allegra/my_scripts
- What is command-line completion?
- What is a default argument?
Challenge #3 Use a text editor to write commands into a file, save, exit, make it executable and run it
See the Solution to challenge #1
ssh remote_host
The remote_host is the IP address or domain name that you are trying to connect to.
If your username is different on the remote system:
ssh remote_username@remote_host
Once you have connected to the server, you will probably be asked to verify your identity by providing a password.
ssh -x remote_username@remote_host
sftp username@host
Enter your password when prompted
Several Unix commands do work
get: Copy a file from the remote computer to the local computer.
put: Copy a file from the local computer to the remote computer.
scp: copies files over a secure, encrypted network connection.
scp /home/image*.jpg allegra@myhost.com:/home/images
scp allegra@myhost.com:/home/image*.jpg /home/allegra/downloads
scp [-12346BCpqrv] [-c cipher] [-F ssh_config] [-i identity_file]
[-l limit] [-o ssh_option] [-P port] [-S program]
[[user@]host1:]file1 ... [[user@]host2:]file2
Enter your password when prompted
wget [option]... [URL]...
- Non-interactive means that it can work in the background, while the user is not logged on.
- This allows you to start a retrieval and disconnect from the system, letting Wget finish the work.
- By contrast, most of the Web browsers require constant user's presence, which can be a great hindrance when transferring a lot of data.
$ ls -a [Enter]
$ cd . [Enter]
$ cd .. [Enter]
$ ls ~/oeiras
more , less, clear
