Common Terminal Commands

Here is a very brief collection of some commands that you can use in a shell.

The man command

One of the best and easiest ways to learn more about these commands, or to figure out how to use them or what options they support is to use the man command (short for "manual pages").

Just type:

into a shell to open the man pages for a command. It will temporarily "take over" your terminal window, and you can navigate up and down using the arrow keys or the u and d keys. When you're finished, press q to quit. The usefulness of man pages varies, but they may include:

Type:

    man pwd

to see the man pages for the pwd command. Navigate up and down using the arrow keys or the u and d keys. When you are finished, press q to quit.

A Brief Discussion of File Paths

The path to a file or directory (i.e. its location in the file system) can be specified as either absolute or relative. An absolute path leaves no ambiguity about its location, and is defined with the root directory "/" as the reference point. For example, the path:

would be an absolute path.

A relative path, however, is defined from the current directory as a reference point. For example, if you're in a shell and your current directory is /course/cs015/, you could omit that directory when referring to a file that's already in your current directory. So you could refer to a file called:

as just:

You can carry the usefulness of relative paths a little further by digging into directories. For example, if you're in your home directory "/home/<yourlogin>/" and you want to refer to a file called cs015Homework within a directory called cs015files, the absolute path would be:

but the relative path from your current location would just be:

Note that an absolute path always starts from the root directory /, while a relative path does not.

Special Directories: "." and ".."

Linux also provides a way for you to refer to the current directory and it's parent directory when working with relative paths. The symbol . refers to whatever the current directory you're working in is, and .. refers to its parent. For instance, if you want to access a file that is one folder higher than you are right now, you could use the relative path:

It is okay if the different types of file paths seem confusing. The only way to get a good understanding is to use it and ask questions as you go along. You can always refer back to this lab in the future if you want more clarification on a topic.

Short List of Useful Linux Commands

Command What it does Arguments Flags
ls Lists the contents of a directory The path of the directory to list. If none is listed, the contents of the current directory will be listed. -a: Include hidden files
-l: List in "long format" with extra information
cd Change directory (to a new working directory) The path of the directory to change to. A path that starts with a / is called "fully qualified", meaning there is no ambiguity about the location specified. If the path does not start with a /, the path is said to be "relative," and is determined relative to the current location. If no location is specified as an argument, then the new directory will be the home directory. (no common flags)
rm Removes a file The file to be removed -r: Recursively delete files (i.e. allow the deletion of a directory and everything it contains. Directories cannot be deleted with rm without the r flag
mkdir Makes a new directory The name (or full path) of the new directory (no common flags)
rmdir Removes an empty directory The name (or full path) of the directory to be deleted (no common flags)
zwrite Send a message to a user (sort of like IM) The username to send a message to. E.g.:
    zwrite hvjackso
 (no common flags)
touch Creates a new empty text file (among other things) The name (or full path) of the new file. E.g.:
    touch MyNewFile.txt
to name a new file in the current directory, or:
    touch /u/hvjackso/course/cs015/NewFile.java
to make a new file at the specified location. 		(no common flags for making new files)
mv Moves a file from one location to another. This can be used to rename the file. The full or relative path of the existing file, followed by the full or relative path of the new file. Note that the directory can be the same, effectively renaming the file. E.g.
    mv MyOldFile.java MyNewFile.java
just renames the file. 		(no common flags)
cp Copies a file from one location to another (similar to mv) The full or relative path of the existing file, followed by the full or relative path of the new file. Syntax is similar to mv. (no common flags)
finger Look up information about a user The username to look up. E.g.:
    finger hvjackso
 (no common flags)

Don't be intimidated by this list. You definitely do not have to memorize this (that's what the man command is for!).

Try these steps in a terminal window, and follow along to see what's happening.

  • Open a terminal window and type:

      cd

    The cd command (short for "Change Directory") switches the "current directory" of the shell window you're in. If you specify a path after the command you will be switched to that location; otherwise, you'll switch to your home directory. You should see a tilda as part of the command prompt to show you where you are.

  • Type:

      ls

    This command will show you the contents of a directory. If you specify a directory, it will show you the contents of that directory, but otherwise it will show you the contents of the current one.

    In your home directory you should already have a bunch of files. That's fine.

  • Type:

      mkdir NewDirectory

    This will make a new directory in the current location called "NewDirectory"

  • Type:

      ls

    Now you can see it is there. You can tell that it is a directory because it has a / after the name.

  • Type:

      cd NewDirectory

    Notice that the command prompt will change to reflect the new location. Note: file names in Linux are case sensitive; "newdirectory" is not the same as "NewDirectory".

  • Type:

      ls

    This time you will notice that you get no results. Obviously your new directory is empty, so you don't get anything back.

  • Type:

      touch MyNewFile

    then type:

      ls

    Now you can see that your new file called "MyNewFile" is there.

  • Type:

      rm MyNewFile

    This gets rid of the new file you created

  • Type:

      cd ..

    This moves the current directory up a level. You'll see in the command prompt that you're back at your home directory.

  • Type:

      rmdir NewDirectory

    This will remove the directory you originally made.

That's it!