the shell game part 3: introduction to bash

The Shell Game 3

Kevin O'BrienWashtenaw Linux Users Group

http://www.lugwash.org

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The Bourne-Again Shell (bash)● Now that we have looked at some general

ideas about shells, and looked at the choices that are available, it is time to focus on the shell we will use for the rest of the series

● The Bourne-Again Shell (bash) is the default on all Linux systems

● It is as universal as anything can be in the world of Unix-like systems

● So if you only learn one shell, this is the one to learn

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Bash commands

● Most Linux commands are separate files● You can find them by name on your hard drive● You can open a man page for them● But bash commands are all internal to bash● You cannot find them on your hard drive● They do not have a man page● Instead, they are all in the man page for bash

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Examples

Just some of the bash commands

alias bind cd dirs

echo eval exec exit

hash help history jobs

kill logout pwd read

set source suspend times

trap type umask wait

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Navigating

● A good starting point for bash is learning to move around

● This is done with the cd command● Did you note that cd is one of the built-in

commands in bash?● That means the information about it is in the

bash man page

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Cd 1

● This stands for Change Directory● More precisely, it should be Change the

Current Working Directory● This is often the most convenient way to

execute other commands, even if they could be done some other way

● For example, you could change the working directory so that you could then work on a file in that directory

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Cd 2

● The syntax for this command is

cd [option] [directory]

● The arguments in brackets are themselves optional, i.e., you can successfully execute the command without specifying either an option or a directory

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Shortcuts

● In Unix-like operating systems the current directory can be represented by a dot

● The parent directory is represented by two dots

● The home directory is represented by ~ (called a tilde, found in the upper left of the keyboard)

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Cd options

● There are only two, and they are not commonly used (-P, -L)

● These involve either following or not not following symbolic links

● So we won't discuss them further at this time

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Absolute paths● These are paths that begin with the root (/) of

the system● An example might be /home/kevin/Downloads,

which is where all of my downloaded files go● Relative paths are paths relative to the current

working directory● So, if I had a sub-directory of my Downloads

directory, for example Firefox, I could give it the relative path /Firefox if I am in my Downloads directory

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Present Working Directory

● The directory you are currently in is also known as the Present Working Directory

● The command to display this is pwd● Did you notice this is also a built-in bash

command?● This means you can find more info about it in

the bash man page● You may not need this as much if your bash

prompt displays the current directory

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Exercises 1● First, use the pwd command to display your

Present Working Directory● To go to /usr/local/share, type

cd /usr/local/share● To go to your home directory, type

cd ~● To go back to /usr/local/share, type

cd

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Exercises 2

● To go to /usr/local/share/man typecd /man

● To go back to /usr/local/share, typecd ..

● To go the the root of the system, typecd /

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Practice these commands

● To be really proficient you need to have these commands memorized

● They are not all that complicated● Navigation is so essential that you don't want

to be stopping to try and look up how to navigate when you are fixing a problem

● How do you get to Carnegie Hall?

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Resources

● The bash man page (you can also read this online at http://linux.die.net/man/1/bash)

● The Bash Reference Manual at http://www.gnu.org/software/bash/manual/bashref.html

● You have man pages on your computer, and they are there even if you are not connected to the Internet. So get to know how to use the man pages that are already on your hard drive.