To begin
executing programs, click on the icon on the bottom icon bar looking like a
computer screen partially covered by a seashell. This starts up a terminal at
which you will be able to type commands. You can have many such windows open at
any one time.
You begin
typing at the prompt i.e. after the ‘>’ below
/home/your_user_name>
NOTE!!!! These
commands are CASE SENSITIVE!!! Thus, taking the first example given below
> ls
will list the
files in the current directory but
> LS
will not work
When you are
working at the terminal, you are always working in the context of some
particular directory on the computer’s file system. If you type ‘pwd’ at the prompt,
you will be told which directory you are currently in.
You will often
want to know which files are in your current directory. You can do this by
typing either
> ls
or
> ls -l (this is if you want to obtain
additional information about your files, such as when they were created )
You will also
sometimes want to know what is inside a file. You can look (but not change)
what is in the file using either
> less
filename
or
> tail -n30
filename
The programme
‘less’ allows you to scroll around inside a file using the arrow
keys, the space bar and the delete button. The programme ‘tail’ prints out the last lines
in a file (by changing the number after the ‘-n’ you can alter how
many lines at the end to print out
If you want to
change the contents of the file, try the following command:
> emacs
filename &
This executes
the file-editor called ‘emacs’, opening the file called filename in
it to be edited, and by adding the ‘&’ at the end of the
command, you allow emacs to run while allowing you to continue typing at the
terminal. You will often want to use the ‘&’ at the end of a
line when you run an interactive programme but at the same time want to
continue typing at the same terminal. For example, when looking at treefiles
you will usually type
> njplot
treefilename &
You will need
to know a few basic commands in emacs to be able to use it properly.
To save what
you have in the editor at the moment with the same filename as that with which
you executed emacs type
Control-X
and then
Control-S
(usually
written “C-X C-S”)
To write the
contents of the current contents of emacs to a file with a new name type
Control-X
and then
Control-W
(i.e.
“C-X C-W”)
If you are
halfway through a command and you change your mind do
C-G
To close the
emacs window do
C-X C-C
NOTE!!!! It is usually a good idea, if you are
going to edit an important file, to make a copy of the original file (e.g.
“file1” to a file with name something like
“file1_original”, and to only then edit “file1”. That
way, if you make a mistake in ‘file1’ you can always just create again a new copy of
“file1” by copying “file1_original” to a file with name
“file1”.
There are many
different ways of doing this. One of them is to run
> emacs
new_filename &
This will open
emacs with a blank page. You can then type into this page. Then, if you tell
emacs to save the file, a new file with the name new_filename will be created.
You will often
want to change which directory you are currently working in. To do this use the
‘cd’ command. To do this you need to be aware of several different
rules about how the position of files are specified in a linux filesystem.
> cd dirname
will change
your directory to that of directory ‘dirname’ that exists in the
directory you are currently in
> cd
dirname/another_dirname
will change
your directory to that of directory ‘another_dirname’ that is in
the directory ‘dirname’ that is in your current directory
> cd ..
will change
your directory to that of your parent directory i.e. the directory that
contains your current directory
> cd
../a_third_dirname
will change
your directory to that of the directory “a_third_dirname” that is
in your parent directory
> cd
will return you
to your home directory
> cd
~/dir_in_your_home_directory
the
“~” tells the machine that you want to specify a directory name
with respect to your home directory. Thus, you could be in the directory
/tmp/dir3, and type the above command, and then move to the directory
/home/your_user_name/dir_in_your_home_directory
> cd
/tmp/dir3
From anywhere
in the filesystem, this will place
you in the directory /tmp/dir3 - the “/” at the beginning of the
directory name indicates that the name of the directory is being specified to
the lower-most directory in the filesystem, the so-called ‘root’
directory.
> cd /
takes you
straight to the root directory
To create a
copy of file “file1” with the name “file2” in the same
directory as file1 type
> cp file1
file2
To create a
copy of file1 in your parent directory type
> cp file1
../file2
You will notice
that the way that you refer to the parent directory here is exactly the same as
the way in which you refer to the parent directory when trying to move there
(see the section above “changing your position in the filesystem). All
the rules used to specify directories in the filesystem that you read there
apply here also. Thus, for another example
> cp file1
~/dir_in_home_directory/file2
will create a
copy of file1 that will be at the position
/home/your_user_name/dir_in_home_directory/file2
To create a
copy of directory “dir1” in the local directory called
“dir2” type
> cp -r dir1
dir2
To move a file
from name “file1” to name “file2” in your current
directory type
> mv file1
file2
To create a new
directory in your current directory type
> mkdir
new_dir_name
To
remove/delete a file, type
> rm filename
To remove a
directory type
> rm -r
directory_name
BE VERY CAREFUL
BEFORE YOU DELETE A FILE!!!!! ALWAYS THINK TWICE BEFORE YOU ISSUE THESE
COMMANDS
If you want to
put the contents of three files ‘file1’, ‘file2’, and
‘file3’ into a fourth file ‘file4’ such that the order
of the information in file4 will be the contents of file1 followed by file2
followed by file3 then type
> cat file1
file2 file3 > file4
> lpr
file_name
This will print
the file on printer V111, just around the corner from the teaching lab
> pwd
report which
directory you are in
> ls
list the files
in the current directory
> ls -l
list the files
in the current directory, providing more information than with just
‘ls’
> less
filename
look at what is
inside the file whose name is ‘filename’
> tail -n40
filename
print the last
40 lines of the file ‘filename’
> emacs
filename &
edit (i.e.
change the contents of) the file ‘filename’ using the emacs editor,
with the editor running in the background
> mv file1
file2
move
‘file1’ to ‘file2’ (i.e. delete ‘file1’,
and move its contents to a new file called ‘file2’)
> cp file1
file2
create a copy
of ‘file1’ called ‘file2’ in the current directory
> mkdir
dirname
create a new
directory called ‘dirname’
> rm
filename
delete a file
called ‘filename’
> rm -r
dirname
delete a
directory called ‘dirname’
> lpr
filename
print the file
called ‘filename’