UMBC CMSC 202 Computer Science II

Lab1: Introduction to UNIX / Linux at UMBC

You will learn about the following:

• Some essential linux commands
• emacs

Linux Commands

Opening a terminal

In the lab machines, simply run a terminal application. Your home directory and all your files are available without SSH. From a Windows machine at home, a good terminal application to use would be PuTTY. When connecting using PuTTY or another ssh client, connect to the server linux.gl.umbc.edu on port 22 with your UMBC username and password.

At this point, you should see a linux prompt, something like:

A sample terminal session

The linux prompt is a text-based interface for issuing commands to a Linux system. From here, you can change to a different directory, run a program, create a file, edit a file, or just about anything else.

Essential Commands

• ls
  This command lists all of the files and folders in the current directory.
• ls -l
  Lists a long version of the directory contents including permissions, owner, group, filesize, last editted date and filename. Directories at the current level have a 'd' at the beginning of their permissions:
  drwx------ 16 don1 rpc 2048 Jan 24 10:21 202
  While files start with a '-':
  -rw------- 1 don1 rpc 383 Jan 24 11:56 hello.cpp
  
• mkdir cmsc202
  This command will make a directory named 'cmsc202'. If you already know something about Linux and have created a 202 directory elsewhere, then you may skip this command and simply go to that directory (i.e. make directory). You may name your folder something other than 'cmsc202' if you like, but this lab will assume you have named it 'cmsc202'.
• ls cmsc202
  When given a directory name, ls will list the files in that directory (however, no files should be in your cmsc202 directory yet).
• cd cmsc202
  This command will change the current directory to be 'cmsc202'. In other words we will move into the 'cmsc202' directory (i.e. change directory).
• mkdir lab01
  This command will make a new directory named 'lab01' within the 'cmsc202' directory (since that is where we are currently located). Most commands work in the current directory only, unless you explicitly state otherwise. You can think of the file and directory structure as a hierarchy - each directory has "child" directories or files. This also means that most every directory has a "parent" directory.
• cd lab01
  Change into the 'lab01' directory.
• touch Lab01.cpp
  This will create an empty file named 'Lab01.cpp' that you can edit later.
• mv Lab01.cpp lab01.cpp
  Move the file 'Lab01.cpp' in the current directory to 'lab01.cpp' in the current directory. This is essentially renaming the file, but you could also use this command to move the file to a different folder.
• mv lab01.cpp ../
  Move the file 'lab01.cpp' in the current directory into the parent directory. The '../' indicates "one directory up the hierarchy". By setting the destination as a directory, the file will retain its original name, but be moved to the new location. An equivalent instruction would be:
  mv lab01.cpp ../lab01.cpp
• cd ..
  This makes the parent directory the current directory (i.e. changes the directory to be one "up" in the hierarchy). If you were to use ls at this point, you will see the lab01.cpp file located outside of the lab01 directory.
• cp lab01.cpp lab01/lab01.cpp
  This will make a copy of our file from the current directory to the lab01 directory. There are now two identical versions of 'lab01.cpp'.
• cp -r lab01 lab01_new
  Create an exact copy of the entire directory 'lab01' as a new directory 'lab01_new'. If you 'cd' into the new directory, you will find a file there named 'lab01.cpp' - this is an exact copy. The '-r' means "recursively" which means that any directories and files in 'lab01' will be copied over to the new location. This can be particularly important within this class as you will want to copy over all of your project files into a new folder before working on the next project!
• rm lab01.cpp
  Removes the file 'lab01.cpp'. You will be prompted to confirm the deletion of this file. If you would prefer to NOT be prompted, you can use the following:
  rm -f lab01.cpp
  The '-f' will "force" the deletion of the entire folder and its contents.
• rm -r lab01_new
  Removes (recursively) the entire folder and its contents lab01_new. You will be prompted to confirm the deletion of each item. If you would prefer to NOT be prompted, you can use the following:
  rm -rf lab01_new
  An alternative to using 'rm' to remove a directory is to use 'rmdir' (remove directory), but the directory must be empty, 'rmdir' doesn't work with the '-r' switch.
  rmdir lab01_new
• cd ~
  Change directory to your home (initial starting point). '~' always represents your home directory. For example, touch '~/hello' will always create the file hello in your home directory, no matter which directory you are currently in.

Self-Check Questions

1. Create a folder named 'temp'
2. Make 'temp' the current folder
3. Create a file named 'temp.cpp' in the temp folder
4. Move into the parent folder of 'temp'
5. Copy the temp folder and all of its subfolders and files into a new folder named 'temp2'
6. Completely remove the folder 'temp' and the folder 'temp2'

More commands

• less lab01.cpp
  Types the contents of the 'lab01.cpp' file to the screen, one page at a time. Use your arrow keys to navigate.
• cat lab01.cpp
  Types the contents of the 'lab01.cpp' file to the screen all at once.
• passwd
  Lets you change your password by prompting you for your old and new passwords.
• pwd
  Displays the entire path to your current directory.
• man
  
  THIS IS VERY USEFUL!!! Accesses the UNIX manual which describes commands and even C keywords and functions. If you want to learn something about the 'cat' command, simply type man cat and the associated manual page will appear. If you do not remember the command, you can search for a keyword. For example, if you do not know the 'cp' command, search for 'copy' by using man -k copy and that should bring up some associated pages.

If you are still not familiar with the Linux commands here in this lab, it is strongly suggested you give yourself plenty of extra time to start your first project. The learning curve for this environment can be significant for some students.

Emacs

A sample emacs window

First, check out an online emacs reference (Emacs Cheatsheet or the Wikipedia: List of Emacs commands). There are plenty of different online resources than the ones provided and you are encouraged to find one that is the best for you.

You can see that there are quite a few short-cut keys to learn to really master emacs. There is no need to learn all of these except to speed-up your code development. The more you learn, the more quickly you will be able to copy/paste/alter your code. However, let's start with just the basics, you can learn more of these.

• Opening an existing file is easy, at the command prompt, type:
  emacs lab01.cpp
  This will open the 'lab01.cpp' file that you created in step 1.
• Editing a file is even easier, simply start typing
• Saving a file requires typing:
  CTRL-x CTRL-s
• Exiting the editor requires typing:
  CTRL-x CTRL-c
  If you attempt to exit after altering a file but before saving it, you will be prompted to save your work.