OverviewTeaching: 15 min Exercises: 0 minQuestions
How can I create, copy, and delete files and directories?
How can I edit files?Objectives
Create a directory hierarchy that matches a given diagram.
Create files in that hierarchy using an editor or by copying and renaming existing files.
Display the contents of a directory using the command line.
Delete specified files and/or directories.
We now know how to explore files and directories,
but how do we create them in the first place?
Let’s go back to our
data-shell directory on the Desktop
ls -F to see what it contains:
$ ls -F
creatures/ molecules/ pizza.cfg data/ north-pacific-gyre/ solar.pdf Desktop/ notes.txt writing/
Let’s create a new directory called
thesis using the command
(which has no output):
$ mkdir thesis
As you might guess from its name,
mkdir means “make directory”.
thesis is a relative path
(i.e., doesn’t have a leading slash),
the new directory is created in the current working directory:
$ ls -F
creatures/ north-pacific-gyre/ thesis/ data/ notes.txt writing/ Desktop/ pizza.cfg molecules/ solar.pdf
Good Names for Files and Directories
Complicated names of files and directories can make your life very painful when working on the command line. Here we provide a few useful tips for the names of your files from now on.
Don’t use whitespaces.
White spaces can make a name more meaningful but since whitespace is used to break arguments on the command line is better to avoid them on name of files and directories. You can use
_instead of whitespace.
Don’t begin the name with
Commands treat names starting with
Stay with letters, numbers,
May of the others characters have an special meaning on the command line that we will learn during this lesson. Some will only make your command not work at all but for some of them you can even lose some data.
If you need to refer to names of files or directories that have whitespace or another non-alphanumeric character you should put quotes around the name.
However, there’s nothing in it yet:
$ ls -F thesis
Let’s change our working directory to
then run a text editor called Nano to create a file called
$ cd thesis $ nano draft.txt
When we say, “
nanois a text editor,” we really do mean “text”: it can only work with plain character data, not tables, images, or any other human-friendly media. We use it in examples because almost anyone can drive it anywhere without training, but please use something more powerful for real work. On Unix systems (such as Linux and Mac OS X), many programmers use Emacs or Vim (both of which are completely unintuitive, even by Unix standards), or a graphical editor such as Gedit. On Windows, you may wish to use Notepad++. Windows also has a built-in editor called
notepadthat can be run from the command line in the same way as
nanofor the purposes of this lesson.
No matter what editor you use, you will need to know where it searches for and saves files. If you start it from the shell, it will (probably) use your current working directory as its default location. If you use your computer’s start menu, it may want to save files in your desktop or documents directory instead. You can change this by navigating to another directory the first time you “Save As…”
Let’s type in a few lines of text.
Once we’re happy with our text, we can press
Ctrl-O (press the Ctrl or Control key and, while
holding it down, press the O key) to write our data to disk
(we’ll be asked what file we want to save this to:
press Return to accept the suggested default of
Once our file is saved, we can use
Ctrl-X to quit the editor and
return to the shell.
Control, Ctrl, or ^ Key
The Control key is also called the “Ctrl” key. There are various ways in which using the Control key may be described. For example, you may see an instruction to press the Control key and, while holding it down, press the X key, described as any of:
In nano, along the bottom of the screen you’ll see
^G Get Help ^O WriteOut. This means that you can use
Control-Gto get help and
Control-Oto save your file.
nano doesn’t leave any output on the screen after it exits,
ls now shows that we have created a file called
Let’s tidy up by running
$ rm draft.txt
This command removes files (
rm is short for “remove”).
If we run
its output is empty once more,
which tells us that our file is gone:
Deleting Is Forever
The Unix shell doesn’t have a trash bin that we can recover deleted files from (though most graphical interfaces to Unix do). Instead, when we delete files, they are unhooked from the file system so that their storage space on disk can be recycled. Tools for finding and recovering deleted files do exist, but there’s no guarantee they’ll work in any particular situation, since the computer may recycle the file’s disk space right away.
Let’s re-create that file
and then move up one directory to
$ nano draft.txt $ ls
$ cd ..
If we try to remove the entire
thesis directory using
we get an error message:
$ rm thesis
rm: cannot remove `thesis': Is a directory
This happens because
rm by default only works on files, not directories.
To really get rid of
thesis we must also delete the file
We can do this with the recursive option for
$ rm -r thesis
With Great Power Comes Great Responsibility
Removing the files in a directory recursively can be very dangerous operation. If we’re concerned about what we might be deleting we can add the “interactive” flag
rmwhich will ask us for confirmation before each step
$ rm -r -i thesis rm: descend into directory ‘thesis’? y rm: remove regular file ‘thesis/draft.txt’? y rm: remove directory ‘thesis’? y
This removes everything in the directory, then the directory itself, asking at each step for you to confirm the deletion.
Let’s create that directory and file one more time.
(Note that this time we’re running
nano with the path
rather than going into the
thesis directory and running
$ mkdir thesis $ nano thesis/draft.txt $ ls thesis
draft.txt isn’t a particularly informative name,
so let’s change the file’s name using
which is short for “move”:
$ mv thesis/draft.txt thesis/quotes.txt
The first parameter tells
mv what we’re “moving”,
while the second is where it’s to go.
In this case,
which has the same effect as renaming the file.
ls shows us that
thesis now contains one file called
$ ls thesis
One has to be careful when specifying the target file name, since
silently overwrite any existing file with the same name, which could
lead to data loss. An additional flag,
mv -i (or
can be used to make
mv ask you for confirmation before overwriting.
Just for the sake of inconsistency,
mv also works on directories — there is no separate
quotes.txt into the current working directory.
mv once again,
but this time we’ll just use the name of a directory as the second parameter
mv that we want to keep the filename,
but put the file somewhere new.
(This is why the command is called “move”.)
In this case,
the directory name we use is the special directory name
. that we mentioned earlier.
$ mv thesis/quotes.txt .
The effect is to move the file from the directory it was in to the current working directory.
ls now shows us that
thesis is empty:
$ ls thesis
ls with a filename or directory name as a parameter only lists that file or directory.
We can use this to see that
quotes.txt is still in our current directory:
$ ls quotes.txt
cp command works very much like
except it copies a file instead of moving it.
We can check that it did the right thing using
with two paths as parameters — like most Unix commands,
ls can be given thousands of paths at once:
$ cp quotes.txt thesis/quotations.txt $ ls quotes.txt thesis/quotations.txt
To prove that we made a copy,
let’s delete the
quotes.txt file in the current directory
and then run that same
$ rm quotes.txt $ ls quotes.txt thesis/quotations.txt
ls: cannot access quotes.txt: No such file or directory thesis/quotations.txt
This time it tells us that it can’t find
quotes.txt in the current directory,
but it does find the copy in
thesis that we didn’t delete.
What’s In A Name?
You may have noticed that all of Nelle’s files’ names are “something dot something”, and in this part of the lesson, we always used the extension
.txt. This is just a convention: we can call a file
mythesisor almost anything else we want. However, most people use two-part names most of the time to help them (and their programs) tell different kinds of files apart. The second part of such a name is called the filename extension, and indicates what type of data the file holds:
.txtsignals a plain text file,
.cfgis a configuration file full of parameters for some program or other,
.pngis a PNG image, and so on.
This is just a convention, albeit an important one. Files contain bytes: it’s up to us and our programs to interpret those bytes according to the rules for plain text files, PDF documents, configuration files, images, and so on.
Naming a PNG image of a whale as
whale.mp3doesn’t somehow magically turn it into a recording of whalesong, though it might cause the operating system to try to open it with a music player when someone double-clicks it.
Suppose that you created a
.txtfile in your current directory to contain a list of the statistical tests you will need to do to analyze your data, and named it:
After creating and saving this file you realize you misspelled the filename! You want to correct the mistake, which of the following commands could you use to do so?
cp statstics.txt statistics.txt
mv statstics.txt statistics.txt
mv statstics.txt .
cp statstics.txt .
Moving and Copying
What is the output of the closing
lscommand in the sequence shown below?
$ mkdir recombine $ mv proteins.dat recombine $ cp recombine/proteins.dat ../proteins-saved.dat $ ls
Organizing Directories and Files
Jamie is working on a project and she sees that her files aren’t very well organized:
$ ls -F
analyzed/ fructose.dat raw/ sucrose.dat
sucrose.datfiles contain output from her data analysis. What command(s) covered in this lesson does she need to run so that the commands below will produce the output shown?
$ ls -F
$ ls analyzed
Copy with Multiple Filenames
cpdo when given several filenames and a directory name, as in:
$ mkdir backup $ cp thesis/citations.txt thesis/quotations.txt backup
cpdo when given three or more filenames, as in:
$ ls -F
intro.txt methods.txt survey.txt
$ cp intro.txt methods.txt survey.txt
Listing Recursively and By Time
ls -Rlists the contents of directories recursively, i.e., lists their sub-directories, sub-sub-directories, and so on in alphabetical order at each level. The command
ls -tlists things by time of last change, with most recently changed files or directories first. In what order does
ls -R -tdisplay things?
Creating Files a Different Way
We have seen how to create text files using the
nanoeditor. Now, try the following command in your home directory:
$ cd # go to your home directory $ touch my_file.txt
What did the touch command do? When you look at your home directory using the GUI file explorer, does the file show up?
ls -lto inspect the file’s. How large is
When might you want to create a file this way?
Moving to the Current Folder
After running the following commands, Jamie realizes that she put the files
maltose.datinto the wrong folder:
$ ls -F raw/ analyzed/ $ ls -F analyzed fructose.dat glucose.dat maltose.dat sucrose.dat $ cd raw/
Fill in the blanks to move these files to the current folder (i.e., the one she is currently in):
$ mv ___/sucrose.dat ___/maltose.dat ___
cp old newcopies a file.
mkdir pathcreates a new directory.
mv old newmoves (renames) a file or directory.
rm pathremoves (deletes) a file.
rmdir pathremoves (deletes) an empty directory.
Use of the Control key may be described in many ways, including
The shell does not have a trash bin: once something is deleted, it’s really gone.
Nano is a very simple text editor: please use something else for real work.