Difference between revisions of "Shell"

From Coder Merlin
 
(33 intermediate revisions by 11 users not shown)
Line 2: Line 2:
{{MerlinCurriculumData|{{ROOTPAGENAME}}}}
{{MerlinCurriculumData|{{ROOTPAGENAME}}}}


== The Client and the Server ==
== Experience ==
[[File:Client-server-model.svg|thumb|link=|Client-server-model]] A '''client-server model''' is a means of distributing resources between the provider of a '''service''' and a consumer of that service, the client.  You're likely very familiar with this concept though less familiar with the name.  One common example of a service provided in this manner is email.  You, a '''user''', can open an email '''client''' (for example, an app on your iPhone or Outlook on a PC) which then connects to a remote '''server'''.  The ''server'' is responsible for providing several ''services'', including receiving mail on your behalf from other servers, transmitting email on your behalf to others, and storing your email for your later use.
{{MerlinMultipageExperienceSubpages
 
|Pages=Client and Server;First Connection;The Shell;Terminating a Partial Command;Directories;Tab Completion;Recall Previous Commands;Alter Previous Commands;Files;Deleting a File;Renaming a File;Directories Revisited;Clear the Screen;Jobs;Change Your Password;Display a Manual;Exiting the Shell
{{Observe|: Section 1|
# Name at least two other services that you personally use which are implemented using a Client/Server Model
}}
 
There are several advantages to this model:
* Users don't need to personally possess the hardware required to fulfill a particular service, only a means of connecting and communicating with a server which provides the service
* Users don't need to worry about installing and configuring the server hardware
* Users are able to access their data from anywhere in the world (as long as they have internet access)
* The state of a users data remains consistent, regardless of how and from where they access the server
 
Merlin is built upon this Client/Server Model, so you won't need any particular type of hardware or software, only a device capable of running a web-browser and a terminal emulator (available in Google Chrome).
 
== First Connection ==
Coder Merlin is a cloud-based server where we’ll be doing most of our exercises.  To access Merlin, you’ll need a '''secure shell client'''. 
 
If you’re using a Mac or a Linux based device you’ll probably have a built-in client that you can access from the terminal. 
 
If you’re using a Windows-based device, you can access a terminal by installing Google Chrome, and then within Google Chrome typing “Secure Shell Extension” and then installing the extension.
 
Either way, you’ll need a connection string to access the server.  The connection string will begin with your first name and last name separated by a hyphen, for example: '''john-williams'''.  The rest of the connection string will be '''@ssh.codermerlin.com'''
 
For John Williams, the entire connection string would be:
{{ConsoleLine||john-williams@ssh.codermerlin.com}}
 
After you’re connected, you’ll be prompted to enter your password.  After a successful logon, you'll land in the "shell".
 
 
{{Hint|
You won't see your password being echoed to the terminal as you type it.  This occurs to keep others from easily seeing your password.  Just pretend that your keypresses are being received correctly.}}
 
 
{{Caution|
The correct connection string, like many identifiers that you'll encounter in computer science, must be entered exactly.  There is no tolerance for any variance.  As such, pay close attention to the requirements.  If you make a mistake, you may be locked out of the server for a period of time.  If this happens, verify the connection string and your password, wait a while, then try again.}}
 
== The Shell ==
A shell is a user interface which provides access to an operating system’s services. There are two basic types of shells: a “command-line interface” (CLI) and a “graphical user interface” (GUI). You are likely familiar with common GUI’s from Microsoft Windows and perhaps Apple’s macOS. This document will focus on a CLI known as '''bash''', a shell for the Unix operating system by Brian Fox. The shell is an acronym for Bourne-again shell, named for the Bourne shell that it replaces.
Login to the Merlin Server as discussed previously. After some introductory text, you’ll see a '''prompt''' (letting you know that the server is ready and waiting for your input) which will look something like this:
{{ConsoleLine|john-williams@codermerlin:~$|}}
You’ll see your login name, an at (@) sign, the name of the server (“codermerlin”), a colon (:), a tilde (~), and a $. This will be followed by a flashing block called a '''cursor'''. The cursor indicates where new characters will appear as you type. The cursor will continue to flash patiently as it awaits input. We’ll get back to the meaning of the tilde soon.
 
We'll be using a server running Linux, a Unix-like operating system.  Almost everything in Unix is either a file or a process. A '''file''' is either a destination or source for a stream of data. A '''process''' is a program that is being executed by the operating system. While printers and screens are considered to be “files” in Unix, a more general way of thinking of files is a collection of data that can be referred to by name. Files can be created by users directly (for example, via a text editor) or indirectly, such as the result of running a program like a compiler.
 
== Terminating a Partial Command ==
If you begin a command in error or change your mind about issuing a command, you can use the {{SpecialKey|CONTROL|C}} key sequence to cancel what you've typed so far and continue with a new command prompt.
 
Try it now:
{{ConsoleLine|john-williams@codermerlin:~$ |echo iThoughtIKnewWhatIWasDoingBut {{SpecialKey|CONTROL|C}} }}
 
 
{{Hint|
If you began issuing a command but need to do something else in the shell before actually issuing it, an alternative to the above is to temporarily store what you've typed so far, do something else, then return to the original command.  You can do that with:
{{{Bar}}  class{{Equal}}"wikitable"
    {{Bar}}{{SpecialKey|CONTROL|U}}
    {{Bar}} Cut backwards
{{Bar}}-
    {{Bar}}{{SpecialKey|CONTROL|Y}}
    {{Bar}} Yank the original text back
{{Bar}}}
 
}}
 
== Directories ==
=== Directory Hierarchy ===
[[File:LinuxFileHierarchy.png|thumb|link=|Linux File Hierarchy]]
All files are integrated into a single, hierarchical directory structure that appears as an inverted tree.  A '''directory''' provides a logical grouping of related files (and potentially other directories).  The top of this tree is called the '''root''' and is referred to by a slash (/). In the diagram, we see that the root contains five '''subdirectories''' (i.e., a directory below the parent directory):
bin, etc, home, lib, and tmp. The home directory contains two subdirectories, jack-williams and john-williams. Note that this differs from a Windows file structure as Unix integrates all files into a single directory structure rather than listing different physical storage devices. Thus, the file structure is '''logical''' rather than '''physical'''.  A '''path''' describes an ordered transition through one or more directories on the way to a destination (either a directory or a file).  As such, note that while both jack-williams and john-williams each have a subdirectory named "projects" these are ''different'' directories.  The path to the former is "/home/jack-williams/projects" while the path to the latter is "/home/john-williams/projects".  Paths which begin at the root (symbolized by the initial slash) are called '''absolute paths'''.  All other paths are '''relative paths'''.
 
 
{{Observe|: Section 2|
# It appears that both Jack Williams and John Williams can have a directory of the same name.  Do you think the ability to have two different users create a directory of the same name is important?  Why?
}}
}}


=== Display the Working Directory (Where am I?) ===
The shell uses a concept known as your '''working directory''', which can be thought of as your current directory, i.e. where you are currently located in the file system. If you forget where you are, you can always use the command '''pwd''' to print the working directory. Try it now. Type “pwd” followed by <RETURN>. Note that you’ll need to press <RETURN> after any command before the shell will execute the command.
{{ConsoleLine|john-williams@codermerlin:~$ |pwd}}
{{ConsoleLine|/home/john-williams|}}
The command will print something similar to “/home/john-williams” and then present you with a new prompt and cursor to indicate that it’s ready and awaiting your input. This directory is your '''home directory''' and it has a special symbol, the '''tilde''' (~).
{{Observe|: Section 3|
# Why do you think the home directory has a special symbol to represent it?
}}
=== Create a New Directory ===
In order to keep our Merlin Missions organized, let’s place them all under a directory named “Merlin”. To make a new directory, we’ll use the command '''mkdir''' to which we’ll provide a single argument, the name of the directory that we want to create. Try it now. Type “mkdir Merlin” followed by <RETURN>.
{{ConsoleLine|john-williams@codermerlin:~$ |mkdir Merlin}}
=== Display the Contents of a Directory ===
How do we find out what’s contained in our current directory? We can use the '''ls''' (that’s a lowercase ‘L’ followed by a lowercase ’S’) command to list the directory contents. Try it now. Type “ls” followed by return.
{{ConsoleLine|john-williams@codermerlin:~$ |ls}}
The command will print the contents of the current directory (in this case our home directory) which will include the single directory, “Merlin”, that we created earlier.
=== Change to a New Directory ===
When we want to change our current directory we use the '''cd''' command followed by the name of the directory to which we want to change. Try it now. Type “cd Merlin”.
{{ConsoleLine|john-williams@codermerlin:~$ |cd Merlin}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |}}
{{Observe|: Section 4|
# Did the prompt change?  If so, how?  Why is this useful?
}}
Note that our prompt has now changed. Before the command was executed, the prompt contained a single tilde indicating that our home directory was our current directory. After executing the command our prompt now includes a tilde, followed by a slash, followed by “Merlin”. This indicates that we are in the directory named “Merlin” below our home directory. The slash is a '''delimiter''' separating the levels of our hierarchy.
Let’s try the ''pwd'' command again.
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |pwd}}
We can now see that from the root, we’re three levels down:<br/>
/ (root)<br/>
home<br/>
john-williams<br/>
Merlin<br/>
The ''cd'' command has a useful shortcut. If we type the command without an argument, it will take us back to our home directory. It’s the equivalent of "cd ~". Let’s try it now:
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |cd}}
{{ConsoleLine|john-williams@codermerlin:~$ |}}
Now, move back to the Merlin directory by issuing the appropriate command.
=== Change to a New Directory Temporarily ===
When we want to change our current directory ''temporarily'' (meaning we want to return later to where we are now), we use the '''pushd''' command followed by the name of the directory to which we want to change. Try it now. Type “pushd Merlin”.
{{ConsoleLine|john-williams@codermerlin:~$ |pushd Merlin}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |}}
We can now perform any actions we'd like in this directory and when we're done, we can easily return from whence we came without needing to type in the original directory name.  The '''popd''' command will look up where we came (when we used '''pushd''') and return us to there.  Try it now.  Type '''popd'''.
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |popd}}
{{ConsoleLine|john-williams@codermerlin:~$ |}}
== Tab Completion ==
Very often, the shell can help us to complete file and directory names when we begin to type the name of a file (or directory) and then type {{Key|TAB}}. Try it now. Type "cd M" and then press {{Key|TAB}}. The shell will complete the rest of the name by appending "erlin" to what you’ve already typed. Then press {{Key|ENTER}}. Because the completion is not ambiguous (i.e. there is only one solution) the shell will complete the name. If there were multiple possibilities, the shell would complete as much as possible and then beep. At this point, we could press {{Key|TAB}} twice in succession to see the possible completions. Let’s try this. Within the Merlin directory, create three new directories: hello, hello2, and hello3:
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |mkdir hello}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |mkdir hello2}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |mkdir hello3}}
Then, type “cd h”:
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |cd h}}
Now, press {{Key|TAB}}.  The shell will complete as much of the name as possible and then beep. (Depending on your terminal you may not hear the beep or you may see a flash.)
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |cd hello}}
Now press {{Key|TAB}} twice in succession. The shell will display matching possibilities and then provide a new prompt followed by the previous entry:
{{ConsoleLine|hello/ hello2/ hello3/|}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |cd hello}}
You now have the option of pressing {{Key|ENTER}} to accept "hello" or adding some more characters (in this case “2” to form “hello2” or “3” to form “hello3”) and then pressing {{Key|ENTER}} to execute the command as-is or {{Key|TAB}} to search for additional completions. In our case, let’s press {{Key|ENTER}} to descend into the "hello" directory:
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |cd hello}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |}}
== Recall Previous Commands ==
Sometimes it's expedient to quickly recall a previous command without the need to re-type it.  The most common means of accomplishing this is to use the up-arrow.  Let's try it:
{{ConsoleLine|john-williams@codermerlin:~$ |ls}}
Now, let's repeat the command, but rather than type '''ls''' again, try typing the up-arrow:
{{ConsoleLine|john-williams@codermerlin:~$ |{{Key|↑}}}}
Try pressing the {{Key|↑}} and {{Key|↓}} several times.
{{Observe|: Section 5|
# What happens each time you press the {{Key|↑}}?
# What happens each time you press the {{Key|↓}}?
}}
== Files ==
=== Echo to the Screen ===
The echo command echoes the argument to the output. Let’s try it. Type: '''echo "Hello, World!"''' The echo command dutifully echoes the argument to the screen. Try it now:
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |echo "Hello, World!"}}
{{ConsoleLine|Hello, World!|}}
=== Create an Empty File ===
The touch command creates a new, empty file, if such a file does not already exist. If such a file does already exist, the access and modification times will be set to the current time.  Try it now:
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |touch newFile.txt}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |ls}}
{{ConsoleLine|newFile.txt|}}
We'll see the '''cat''' command more below, but for now it's enough to understand that it will display the contents of a file.  Because this is a new, empty file, nothing will be displayed.  Try it now:
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |cat newFile.txt}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |}}
=== Redirection ===
Remember that we said that almost everything in Unix is either a file or a process and that the screen could be considered as a file. We can '''redirect''' the output from echo to another file, one that we'll store in the file system. We do this with the > (greater-than) symbol. Normally, commands will send their output to a device called '''stdout'''. This is what the echo command did when we used it earlier. In our case, stdout is printed to our terminal. Let’s try to redirect our output to a file. Type: '''echo "Hello, World!" > out.txt''':
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |echo "Hello, World!" > out.txt}}
{{Observe|: Section 6|
# Was "Hello, World!" printed to the screen as before?  If not, why not?  What do you think happened to the text?
}}
No output was displayed; we just received a new prompt. Let’s use the '''ls''' command to take a look:
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |ls}}
{{ConsoleLine|newFile.txt out.txt|}}
We can see that the directory contains a single file, "out.txt" which was created by the echo command. How can we see what's contained within this file?
=== Quickly View File Contents ===
To quickly view the contents of a file we can use the '''cat''' command.  The cat command '''concatenates''' files together and then sends the output to stdout. (Remember that in our case this is the screen.) Let’s try it. Type "cat out.txt".
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |cat out.txt}}
{{ConsoleLine|Hello, World!|}}
=== Append a Small Amount of Text to an Existing File ===
If we already have an existing file with some text we can '''append''' (add text to the end) of this file by using echo and redirection as before but with ''two'' "greater-than" symbols adjacent to one another.  Try it now.  Type: echo "Hello, again!" >> out.txt
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |echo "Hello, again!" >> out.txt}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |}}
Let’s move back up to our home directory. Remember that we can do this by typing "cd" without any arguments.
{{ConsoleLine|john-williams@codermerlin:~/Merlin/hello$ |cd}}
{{ConsoleLine|john-williams@codermerlin:~$ |}}
== Deleting a File ==
We can delete a file with the '''rm''' (remove) command. Let's try it:
{{ConsoleLine|john-williams@codermerlin:~$ |echo "Hello" > hello.txt }}
{{ConsoleLine|john-williams@codermerlin:~$ |ls }}
{{ConsoleLine|john-williams@codermerlin:~$ |rm hello.txt }}
{{ConsoleLine|john-williams@codermerlin:~$ |ls }}
== Renaming a File ==
We can rename a file with the '''mv''' (move) command. Let's try it:
{{ConsoleLine|john-williams@codermerlin:~$ |echo "Hello" > hello.txt }}
{{ConsoleLine|john-williams@codermerlin:~$ |ls }}
{{ConsoleLine|john-williams@codermerlin:~$ |mv hello.txt goodbye.txt}}
{{ConsoleLine|john-williams@codermerlin:~$ |ls }}
== Directories (Revisited) ==
There are useful shortcuts that you can use when specifying a path.
* "." (a single period or dot) refers to the ''current'' directory
* ".." (a double period, or two adjacent dots) refers to the ''parent'' directory, relative to wherever you happen to be in the path up to this point
Thus:
* To move to a ''parent'' directory, we can type {{Key|c}}{{Key|d}}{{Key|Space}}{{Key|.}}{{Key|.}}
* To move to a ''grandparent'' directory, we can type {{Key|c}}{{Key|d}}{{Key|Space}}{{Key|.}}{{Key|.}}{{Key|/}}{{Key|.}}{{Key|.}}
Assume we have a directory named 'parent' with two children, 'childA' and 'childB', and we are currently inside the 'childB' directory and want to enter the 'childA' directory.
* To move to a ''sibling'' directory, we can type {{Key|c}}{{Key|d}}{{Key|Space}}{{Key|.}}{{Key|.}}{{Key|/}}childA
=== View the Directory Hierarchy ===
Sometimes it’s helpful to obtain an overview of our directory hierarchy. We can do this with the '''tree''' command. Let's try:
{{ConsoleLine|john-williams@codermerlin:~$ |tree}}
{{ConsoleLines|
.<br/>
└─ Merlin<br/>
&nbsp;&nbsp;&nbsp;├─&nbsp;hello<br/>
&nbsp;&nbsp;&nbsp;│&nbsp;&nbsp;├─ newFile.txt<br/>
&nbsp;&nbsp;&nbsp;│&nbsp;&nbsp;└─ out.txt<br/>
&nbsp;&nbsp;&nbsp;├─&nbsp;hello2<br/>
&nbsp;&nbsp;&nbsp;└─&nbsp;hello3<br/>
}}
{{Observe|: Section 7|
# How does the '''ls''' command differ from the '''tree''' command?
# How do you choose to use one over the other?
}}
=== Remove a Directory ===
Let's remove the two directories that we won't be using anymore. We can do this with the '''rmdir''' command. Move to the Merlin directory and then remove the hello2 and hello3 directories. Then do a directory listing to see what’s left.
{{ConsoleLine|john-williams@codermerlin:~$ |cd Merlin}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |rmdir hello2}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |rmdir hello3}}
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |ls}}
{{ConsoleLine|hello|}}
== Clear the Screen ==
In some cases it’s useful to clear the screen. (For example, this might be useful if you sense your guide creeping up behind you when you were doing something that you weren’t supposed to be doing. 😁) We can do this with the clear command. Type '''clear''' and then press {{Key|RETURN}}.
{{ConsoleLine|john-williams@codermerlin:~$ |clear}}
== Jobs ==
A '''program''' is an executable file which contains a series of instructions which can be executed by the computer.  A '''process''' is a ''program'' which is ''being executed'' on the computer.  The shell manages processes using the concept of a '''job'''.  You can obtain a list of jobs and suspend and resume jobs.  This functionality enables you to maximize your use of time rather than wait for the prompt to return as the shell waits for the execution of a job to complete.
=== Identifying Jobs ===
The shell provides several different ways to identify a job:
* <code>%''n''</code> - The specific job number is preceded by a percentage sign
* <code>%+</code> - A shortcut to specify the current job
* <code>%-</code> - A shortcut to specify the previous job
=== Listing Jobs ===
Jobs may be listed with the '''jobs''' command.  Let's try an example by executing a few long-running jobs.  The '''sleep''' command simply waits before returning.  Let's try it:
{{ConsoleLine|john-williams@codermerlin:~$|sleep 3}}
Let's try it again:
{{ConsoleLine|john-williams@codermerlin:~$|sleep 5}}
{{Observe|: Section 8|
# What do you think the argument to sleep specifies?
# Are you able to prove your hypothesis?  How?
}}
These same jobs can be executed in the background (more on this below) simply by specifying an ampersand (&) after the command. 
Let's try it:
{{ConsoleLine|john-williams@codermerlin:~$|sleep 60 &}}
{{Observe|: Section 9|
# How is the behavior different from what you expected?
# What do you think it means to run a job in the background?
# What do you think the number displayed in brackets specifies?
}}
Let's run several jobs in the background and then view a list of our jobs:
{{ConsoleLine|john-williams@codermerlin:~$|sleep 40 &}}
{{ConsoleLine|john-williams@codermerlin:~$|sleep 30 &}}
{{ConsoleLine|john-williams@codermerlin:~$|sleep 20 &}}
Now, let's use the '''jobs''' command:
{{ConsoleLine|john-williams@codermerlin:~$|jobs}}
Repeatedly execute the '''jobs''' command.
{{Observe|: Section 10|
# What do you observe as you execute the '''jobs''' command?
# How do you explain your observations?
}}
=== Terminating a Job ===
While a job is executing, we may decide that we want to terminate it.  Perhaps it is taking too long or we began executing it with the wrong arguments.  We can often terminate the job with a special key sequence, {{SpecialKey|CONTROL|C}}.
Let's try an example.  We'll execute the '''cat''' command without any arguments, which will cause it to wait for something to be entered on the console. 
{{ConsoleLine|jane-williams@codermerlin:~$|cat}}
The process is now waiting.  If we realize that we made a mistake (perhaps we wanted to print the contents of a file and forgot to specify the file's name) we can terminate the job.  Try it now by pressing {{SpecialKey|CONTROL|C}}.
=== Foreground Jobs ===
Generally, when we execute a program we run it in the '''foreground'''.  This means that our shell will execute the process and we won't be able to execute the next command until the currently running foreground process exits.  This is ideal for short, interactive programs.  Whenever we execute a program, running that program in the foreground is the default.  For example, the '''find''' command can search for all files and directories within our home directory.  Let's try it:
{{ConsoleLine|jane-williams@codermerlin:~/Merlin$|cd}}
{{ConsoleLine|jane-williams@codermerlin:~/Merlin$|find}}
We'll likely see a long list of files and directories quickly scroll by.  But what if we want to generate a list of all of the files and directories on the entire server?  This can take a while. Let's try it, just for fun:
{{ConsoleLine|jane-williams@codermerlin:~/Merlin$|find /}}
Eventually we'll encounter a permissions error and the process will halt.  But if you don't have the patience to wait, remember that you can use the key sequence {{SpecialKey|CONTROL|C}} to terminate the process immediately.  Alternatively, we can use the key sequence {{SpecialKey|CONTROL|Z}} to ''suspend'' the process.  When we suspend a process we can resume it in the foreground with '''fg''' followed by the job number.
=== Background Jobs ===
When we have a complex process that will take a long time to execute we don't want to be blocked from executing other commands while we wait for the long-running process to finish.  In these cases, we can execute the long-running process in the '''background'''.  Running the program in the background means that the process will continue to execute but we'll be able to enter new commands immediately.  We saw an example of this above where we executed multiple '''sleep''' jobs simultaneously.  We were able to do so because the shell was ready to accept new input ''before'' the previous job completed.
We can begin a job in the background by using an ampersand (&) after typing the command.  When we suspend a process we can resume it in the background with '''bg''' followed by the job number.
== Change Your Password ==
When you first log on to the server you'll have been assigned a password.  You should change this password to something that is easy for you to remember but difficult for others to guess (or derive).  (A good summary article of how to select strong passwords may be found [https://www.fpainc.com/blog/password-guidelines-from-nist here].)
The program that you'll use to change your password is '''passwd'''.  It will prompt you three times. 
* You'll first enter your current password
* then the new password that you want to use
* and then finally, to ensure that you're entering the new password correctly, you'll be prompted a second time for the new password.
{{Hint|
Remember that when you enter the password, what you type '''will not be echoed to the terminal'''.  You'll just need to pretend that the your keypresses are being received.
}}
Change your default password to a strong password:
{{ConsoleLines|john-williams@codermerlin:~$ passwd<br/>
Changing password for john-williams.<br/>
(current) UNIX password:<br/>
Enter new UNIX password:<br/>
Retype new UNIX password:<br/>
passwd: password updated successfully
}}
== Display a Manual ==
Finally, let's try out one more very helpful command. If we want to learn more about a command we can read its ''manual''. We do this with the command '''man'''. As an example, look at the man page for the emacs command. Type '''man emacs'''.
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |man emacs}}
The screen will be filled with information about the emacs command. While a man page is displayed we can use the following keys to navigate:
* Typing {{Key|f}} will move us forward one page in the manual
* Typing {{Key|b}} will move us backward one page in the manual
* Typing {{Key|q}} will quit (exit the manual)
Exit the manual now.
== Set Location ==
Some commands (such as '''helpme''', which you'll learn about soon) rely on knowing your location.  Often this is just a room number in a building or simply 'home'.  It's important to set your location.  If you're unsure of the value to use, ask your invigilator.  As an example, to set your location to "Home":
{{ConsoleLine|john-williams@codermerlin:~/Merlin$ |chfn --room Home}}
Note the option "--room" followed by the argument "Home".  This will change your location to "Home".  You can learn more about '''chfn''' by reading the manual.
You'll be prompted for your logon password for confirmation.
== Exiting the Shell ==
In general, there's no need to exit the shell.  It's almost always sufficient to close your terminal emulator.  An advantage to this approach is that the next time you connect to the server you'll be in exactly the same place where you left off.  However, on rare occasions the terminal emulator can become "confused" and display characters in odd places.  In such a case, there's still no need to exit; instead, use the '''reset''' command.
{{SeeAlso|
{{SeeAlso|
[[Category:Linux||Bash||SSH client||SFTP client]]|
[[Category:Linux||Bash||SSH client||SFTP client]]|
Line 435: Line 24:
== Key Concepts ==
== Key Concepts ==
{{KeyConcepts|
{{KeyConcepts|
* A '''client-server model''' is a means of distributing resources between the provider of a service and a consumer of that service, the client. The advantages of this model include:
* A '''client-server model''' is a means of distributing resources between the provider of a service and a consumer of that service, the client. The advantages of this model include:
** Users don't need to personally possess the hardware and software required to implement the service
** Users don't need to personally possess the hardware and software required to implement the service
** Users don't need to worry about installation and configuration
** Users don't need to worry about installation and configuration
** Users are able to access their data from anywhere in the world  
** Users are able to access their data from anywhere in the world  
** The state of a users data remains consistent, regardless of how and from where they access the server
** The state of a users data remains consistent, regardless of how and from where they access the server
* A '''shell''' is a user interface which provides access to an operating system’s services. There are two basic types of shells:  
* A '''shell''' is a user interface that provides access to an operating system’s services. Two basic types of shells exist:  
** A '''command-line interface''' (CLI)
** A '''command-line interface''' (CLI)
** A '''graphical user interface''' (GUI)
** A '''graphical user interface''' (GUI)
* A '''prompt''' lets you know that the server is ready and waiting for your input
* A '''prompt''' lets you know that the server is ready and waiting for your input
* A '''cursor''' is a flashing block which indicates where new characters will appear as you type
* A '''cursor''' is a flashing block that indicates where new characters will appear as you type
* A '''file''' is either a destination or source for a stream of data
* A '''file''' is either a destination or source for a stream of data
* A '''process''' is a program that is being executed by the operating system
* A '''process''' is a program that is being executed by the operating system
Line 451: Line 40:
** The top of this tree is called the '''root''' and is referred to by a slash (/)
** The top of this tree is called the '''root''' and is referred to by a slash (/)
** A '''subdirectory''' is a directory contained within another directory, called the '''parent directory'''
** A '''subdirectory''' is a directory contained within another directory, called the '''parent directory'''
** On Unix systems, the file structure is ''logical'' rather than ''physical''
** On Unix systems, the file structure is '''logical''' rather than '''physical'''
** A '''path''' describes an ordered transition through one or more directories on the way to a destination (either a directory or a file)
** A '''path''' describes an ordered transition through one or more directories on the way to a destination (either a directory or a file)
*** Paths which begin at the root (symbolized by the initial slash) are called '''absolute paths'''
*** Paths that begin at the root (symbolized by the initial slash) are called '''absolute paths'''
*** All other paths are '''relative paths'''
*** All other paths are '''relative paths'''
** Your '''home directory''' is indicated by a special symbol, the ''tilde'' (~)
** Your '''home directory''' is indicated by a special symbol, the ''tilde'' (~)
Line 462: Line 51:
** The command '''cd''' changes your working directory
** The command '''cd''' changes your working directory
** The command '''pushd''' changes our working directory temporarily  
** The command '''pushd''' changes our working directory temporarily  
** The command '''popd''' returns us to our previous directory after executing pushd
** The command '''popd''' returns you to your previous directory after executing pushd
** The command '''tree''' displays a directory hierarchy
** The command '''tree''' displays a directory hierarchy
** The command '''rmdir''' removes (deletes) a directory
** The command '''rmdir''' removes (deletes) a directory
* The '''echo''' command echoes the argument to the output
* The '''echo''' command echoes the argument to the output
* The '''touch''' command creates a new, empty file, if such a file does not already exist. If such a file does already exist, the access and modification times will be set to the current time.
* The '''touch''' command creates a new, empty file, if such a file does not exist. If such a file does exists, the access and modification times will be set to the current time.
* The greater-than symbol (>) can be used to ''redirect'' output to a file
* The greater-than symbol (>) can be used to '''redirect''' output to a file
* Two greater-than symbols (>>) can be used to ''append'' output to a file
* Two greater-than symbols (>>) can be used to '''append''' output to a file
* The '''cat''' command allows us to quickly view the contents of one or more files
* The '''cat''' command allows you to quickly view the contents of one or more files
* The '''rm''' command is used to remove (delete) a file
* The '''rm''' command is used to remove (delete) a file
* The '''mv''' command is used to either move or rename a file
* The '''mv''' command is used to either move or rename a file
* The '''clear''' command clears the screen
* The '''clear''' command clears the screen
* A '''program''' is an executable file which contains a series of instructions which can be executed by the computer
* A '''program''' is an executable file that contains a series of instructions that the computer can execute
* A '''process''' is a program which is ''being executed'' on the computer
* A '''process''' is a program that is ''being executed'' on the computer
* The shell manages processes using '''jobs'''
* The shell manages processes using '''jobs'''
* The '''jobs''' command will list the current jobs associated with your shell
* The '''jobs''' command lists the current jobs associated with your shell
** A job can be terminated by using the key sequence {{SpecialKey|CONTROL|C}}
** A job can be terminated by using the key sequence {{SpecialKey|CONTROL|C}}
** A job can be suspended by using the key sequence {{SpecialKey|CONTROL|Z}}
** A job can be suspended by using the key sequence {{SpecialKey|CONTROL|Z}}
Line 490: Line 79:
<hr/>
<hr/>
''After completing W1005:''
''After completing W1005:''
* {{Assignment|J1002}} Create a journal and answer all questions in this experience. Be sure to include all sections of the journal, properly formatted. 
* {{JournalAssignment|J1002}}
<hr/>
<hr/>
''After completing W1008:''
''After completing W1008:''
* {{Assignment|M1002-10}} Complete {{MMM}} Mission M1002-10.
* {{MMMAssignment|M1002-10}}
* {{Assignment|M1002-31}} Verify your journal's conformance with {{MMM}} Mission M1002-31.
* {{MMMAssignment|M1002-31}}
}}
}}
{{Experience
{{Experience
|experienceID=W1002
|experienceID=W1002
|nextExperienceID=W1003
|experienceUnit=Lab basics
|experienceUnit=Lab basics
|knowledgeAndSkills=§10.121
|knowledgeAndSkills=§10.121
|topicAreas=SSH clients;Linux;Bash
|topicAreas=Bash;Linux;SSH clients
|classroomTime=1 hour
|classroomTime=1 hour
|studyTime=3 hours
|studyTime=3 hours
|acquiredKnowledge=differentiate between a CLI and GUI;
|acquiredKnowledge=differentiate between a CLI and GUI;
understand files, directories, and their organizational hierarchy;
understand files, directories, and their organizational hierarchy;
understand of the client-server model;
understand the client-server model;
understand processes;
understand processes;
understand the purpose of a prompt and cursor
understand the purpose of a prompt and cursor
Line 514: Line 103:
ability to delete files and directories;
ability to delete files and directories;
ability to move and rename files and directories;
ability to move and rename files and directories;
ability to successfully determine location in the file hierarchy;
ability to successfully determine your location in the file hierarchy;
ability to successfully navigate the file hierarchy;
ability to successfully navigate the file hierarchy;
ability to suspend and resume processes;
ability to suspend and resume processes;
ability to terminate processes;
ability to terminate processes;
}}
}}

Latest revision as of 13:36, 12 February 2023

Within these castle walls be forged Mavens of Computer Science ...
— Merlin, The Coder

Curriculum[edit]

ExercisesIcon.png
  Coder Merlin™  Computer Science Curriculum Data

Unit: Lab basics

Experience Name: Shell (W1002)

Next Experience: Help Me! (W1003)

Knowledge and skills:

  • §10.121 Demonstrate proficiency in managing files and processes using a command line interface

Topic areas: SSH clients; Linux; Bash

Classroom time (average): 60 minutes

Study time (average): 180 minutes

Successful completion requires knowledge: differentiate between a CLI and GUI; understand the purpose of a prompt and cursor; understand files, directories, and their organizational hierarchy; understand processes; understand the client-server model

Successful completion requires skills: ability to successfully navigate the file hierarchy; ability to create new, empty files; ability to create new text files; ability to append text to an existing file; ability to move and rename files and directories; ability to delete files and directories; ability to suspend and resume processes; ability to terminate processes; ability to successfully determine your location in the file hierarchy

Experience[edit]


Start One page


👀 See Also[edit]

📺 Videos[edit]

Bash Terminal Beginner's Guide
Linus Torvalds

📖 Texts[edit]

Help Me!
Shell

📚 References[edit]


Key Concepts[edit]

Key ConceptsKeyConceptsIcon.png
  • A client-server model is a means of distributing resources between the provider of a service and a consumer of that service, the client. The advantages of this model include:
    • Users don't need to personally possess the hardware and software required to implement the service
    • Users don't need to worry about installation and configuration
    • Users are able to access their data from anywhere in the world
    • The state of a users data remains consistent, regardless of how and from where they access the server
  • A shell is a user interface that provides access to an operating system’s services. Two basic types of shells exist:
    • A command-line interface (CLI)
    • A graphical user interface (GUI)
  • A prompt lets you know that the server is ready and waiting for your input
  • A cursor is a flashing block that indicates where new characters will appear as you type
  • A file is either a destination or source for a stream of data
  • A process is a program that is being executed by the operating system
  • All files are integrated into a single, hierarchical structure called a directory
    • A directory provides a logical grouping of related files (and potentially other directories)
    • The top of this tree is called the root and is referred to by a slash (/)
    • A subdirectory is a directory contained within another directory, called the parent directory
    • On Unix systems, the file structure is logical rather than physical
    • A path describes an ordered transition through one or more directories on the way to a destination (either a directory or a file)
      • Paths that begin at the root (symbolized by the initial slash) are called absolute paths
      • All other paths are relative paths
    • Your home directory is indicated by a special symbol, the tilde (~)
    • Your working directory can be thought of as your current directory
    • The command pwd prints the working directory
    • The command mkdir creates a new directory
    • The command ls lists the contents of a directory
    • The command cd changes your working directory
    • The command pushd changes our working directory temporarily
    • The command popd returns you to your previous directory after executing pushd
    • The command tree displays a directory hierarchy
    • The command rmdir removes (deletes) a directory
  • The echo command echoes the argument to the output
  • The touch command creates a new, empty file, if such a file does not exist. If such a file does exists, the access and modification times will be set to the current time.
  • The greater-than symbol (>) can be used to redirect output to a file
  • Two greater-than symbols (>>) can be used to append output to a file
  • The cat command allows you to quickly view the contents of one or more files
  • The rm command is used to remove (delete) a file
  • The mv command is used to either move or rename a file
  • The clear command clears the screen
  • A program is an executable file that contains a series of instructions that the computer can execute
  • A process is a program that is being executed on the computer
  • The shell manages processes using jobs
  • The jobs command lists the current jobs associated with your shell
    • A job can be terminated by using the key sequence CONTROL-C
    • A job can be suspended by using the key sequence CONTROL-Z
    • A job can be resumed in the foreground with fg
    • A job can be resumed in the background with bg
  • The man command displays the contents of a manual
  • The reset command resets your terminal

Exercises[edit]

ExercisesExercisesIcon.png

Using pencil and paper, answer all questions in this experience.

After completing W1005:

  •  J1002  Create a journal and answer all questions in this experience. Be sure to:
    • edit your journal using emacs within your ~/Journals directory
    • properly name your journal as J1002.txt
    • include all sections of the journal, properly formatted
    • push your changes to GitHub
    • properly tag your journal as J1002.Final
    • push your tag to GitHub

After completing W1008:

  •  M1002-10  Complete  Merlin Mission Manager  Mission M1002-10.
  •  M1002-31  Complete  Merlin Mission Manager  Mission M1002-31.


Experience Metadata

Experience ID W1002
Next experience ID W1003
Unit Lab basics
Knowledge and skills §10.121
Topic areas Bash
Linux
SSH clients
Classroom time 1 hour60 minutes <br />
Study time 3 hours180 minutes <br />
Acquired knowledge differentiate between a CLI and GUI
understand files, directories, and their organizational hierarchy
understand the client-server model
understand processes
understand the purpose of a prompt and cursor
Acquired skill ability to append text to an existing file
ability to create new text files
ability to create new, empty files
ability to delete files and directories
ability to move and rename files and directories
ability to successfully determine your location in the file hierarchy
ability to successfully navigate the file hierarchy
ability to suspend and resume processes
ability to terminate processes
Additional categories
Retrieved from "https://www.codermerlin.academy/wiki/index.php?title=Shell&oldid=18313"