Creating directories
We now know how to explore files and directories, but how do we create them in the first place?
In this episode we will learn about creating and moving files and directories, using the exercise-data/writing
directory as an example.
Step one: see where we are and what we already have
We should still be in the shell-lesson-data
directory on in our home folder, which we can check using:
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/home/username/shell-lesson-data |
Next we’ll move to the exercise-data/writing
directory and see what it contains:
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cd exercise-data/writing/
ls -F |
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haiku.txt LittleWomen.txt |
Create a directory
Let’s create a new directory called thesis
using the command mkdir thesis
(which has no output):
As you might guess from its name, mkdir
means ‘make directory’. Since thesis
is a relative path (i.e., does not have a leading slash, like /what/ever/thesis
), the new directory is created in the current working directory:
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haiku.txt LittleWomen.txt thesis/ |
Since we’ve just created the thesis
directory, there’s nothing in it yet:
Note that mkdir
is not limited to creating single directories one at a time. The -p
option allows mkdir
to create a directory with nested subdirectories in a single operation:
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mkdir -p ../project/data ../project/results |
The -R
option to the ls
command will list all nested subdirectories within a directory. Let’s use ls -FR
to recursively list the new directory hierarchy we just created in the project
directory:
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ls -FR ../project |
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../project/:
data/ results/
../project/data:
../project/results: |
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TWO WAYS OF DOING THE SAME THINGUsing the shell to create a directory is no different than using a file explorer. If you open the current directory using your operating system’s graphical file explorer, the thesis directory will appear there too. While the shell and the file explorer are two different ways of interacting with the files, the files and directories themselves are the same. |
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GOOD NAMES FOR FILES AND DIRECTORIESComplicated names of files and directories can make your life painful when working on the command line. Here we provide a few useful tips for the names of your files and directories. Don’t use spaces.
Spaces can make a name more meaningful, but since spaces are used to separate arguments on the command line it is better to avoid them in names of files and directories. You can use - or _ instead (e.g. north-pacific-gyre/ rather than north pacific gyre/ ). To test this out, try typing mkdir north pacific gyre and see what directory (or directories!) are made when you check with ls -F . Don’t begin the name with - (dash).
Commands treat names starting with - as options. Stick with letters, numbers, . (period or ‘full stop’), - (dash) and _ (underscore).
Many other characters have special meanings on the command line. We will learn about some of these during this lesson. There are special characters that can cause your command to not work as expected and can even result in data loss. If you need to refer to names of files or directories that have spaces or other special characters, you should surround the name in quotes ("" ). |
Create a text file
Let’s change our working directory to thesis
using cd
, then run a text editor called Nano to create a file called draft.txt
, before we can use Nano, we need to activate it with the module command:
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module load nano
cd thesis
nano draft.txt |
(Details of the module command is covered later)
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WHICH EDITOR?When we say, ‘nano is 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 it is one of the least complex text editors. However, because of this trait, it may not be powerful enough or flexible enough for the work you need to do after this workshop. On Unix systems (such as Linux and macOS), many programmers use Emacs or Vim (both of which require more time to learn), or a graphical editor such as Gedit or VScode. On Windows, you may wish to use Notepad++. Windows also has a built-in editor called notepad that can be run from the command line in the same way as nano for 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 will be asked to provide a name for the file that will contain our text. Press Return to accept the suggested default of draft.txt.
Once our file is saved, we can use Ctrl+X to quit the editor and return to the shell.
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CONTROL, CTRL, OR ^ KEYThe 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: Control-X
Control+X
Ctrl-X
Ctrl+X
^X
C-x
In nano, along the bottom of the screen you’ll see ^G Get Help ^O WriteOut . This means that you can use Control-G to get help and Control-O to save your file. |
nano
doesn’t leave any output on the screen after it exits, but ls
now shows that we have created a file called draft.txt
:
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CREATING FILES A DIFFERENT WAYWe have seen how to create text files using the nano editor. Now, try the following command: Code Block |
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touch my_file.txt |
What did the touch command do? When you look at your current directory using the GUI file explorer, does the file show up? Use ls -l to inspect the files. How large is my_file.txt ? When might you want to create a file this way?
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The touch command generates a new file called my_file.txt in your current directory. You can observe this newly generated file by typing ls at the command line prompt. my_file.txt can also be viewed in your GUI file explorer. When you inspect the file with ls -l, note that the size of my_file.txt is 0 bytes. In other words, it contains no data. If you open my_file.txt using your text editor it is blank. Some programs do not generate output files themselves, but instead require that empty files have already been generated. When the program is run, it searches for an existing file to populate with its output. The touch command allows you to efficiently generate a blank text file to be used by such programs.
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CREATING FILES A DIFFERENT WAY (CONTINUED)To avoid confusion later on, we suggest removing the file you’ve just created before proceeding with the rest of the episode, otherwise future outputs may vary from those given in the lesson. To do this, use the following command: Code Block |
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$ rm my_file.txt |
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WHAT’S IN A NAME?You may have noticed that all of the files are named ‘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 mythesis or 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: .txt signals a plain text file, .pdf indicates a PDF document, .cfg is a configuration file full of parameters for some program or other, .png is a PNG image, and so on. This is just a convention, albeit an important one. Files merely 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.mp3 doesn’t somehow magically turn it into a recording of whale song, though it might cause the operating system to associate the file with a music player program. In this case, if someone double-clicked whale.mp3 in a file explorer program, the music player will automatically (and erroneously) attempt to open the whale.mp3 file. |
Moving files and Directories
Returning to the shell-lesson-data/exercise-data/writing
directory,
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cd ~/shell-lesson-data/exercise-data-writing |
In our thesis
directory we have a file draft.txt
which isn’t a particularly informative name, so let’s change the file’s name using mv
, which is short for ‘move’:
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mv thesis/draft.txt thesis/quotes.txt |
The first argument tells mv
what we’re ‘moving’, while the second is where it’s to go. In this case, we’re moving thesis/draft.txt
to thesis/quotes.txt
, which has the same effect as renaming the file. Sure enough, ls
shows us that thesis
now contains one file called quotes.txt
:
One must be careful when specifying the target file name, since mv
will silently overwrite any existing file with the same name, which could lead to data loss. By default, mv
will not ask for confirmation before overwriting files. However, an additional option, mv -i
(or mv --interactive
), will cause mv
to request such confirmation.
Note that mv
also works on directories.
Let’s move quotes.txt
into the current working directory. We use mv
once again, but this time we’ll use just the name of a directory as the second argument to tell 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.
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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:
Alternatively, we can confirm the file quotes.txt
is no longer present in the thesis
directory by explicitly trying to list it:
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ls thesis/quotes.txt |
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ls: cannot access 'thesis/quotes.txt': No such file or directory |
ls
with a filename or directory as an argument only lists the requested file or directory. If the file given as the argument doesn’t exist, the shell returns an error as we saw above. We can use this to see that quotes.txt
is now present in our current directory:
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MOVING FILES TO A NEW FOLDERAfter running the following commands, Jamie realizes that she put the files sucrose.dat and maltose.dat into the wrong folder. The files should have been placed in the raw folder. Code Block |
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$ ls -F
analyzed/ raw/
$ ls -F analyzed
fructose.dat glucose.dat maltose.dat sucrose.dat
$ cd analyzed |
Fill in the blanks to move these files to the raw/ folder (i.e. the one she forgot to put them in) Code Block |
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$ mv sucrose.dat maltose.dat ____/____ |
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mv sucrose.dat maltose.dat ../raw |
Recall that .. refers to the parent directory (i.e. one above the current directory) and that . refers to the current directory. |
Copying files and directories
The cp
command works very much like mv
, except it copies a file instead of moving it. We can check that it did the right thing using ls
with two paths as arguments — like most Unix commands, ls
can be given multiple paths at once:
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cp quotes.txt thesis/quotations.txt
ls quotes.txt thesis/quotations.txt |
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quotes.txt thesis/quotations.txt |
We can also copy a directory and all its contents by using the recursive option -r
, e.g. to back up a directory:
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cp -r thesis thesis_backup |
We can check the result by listing the contents of both the thesis
and thesis_backup
directory:
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ls thesis thesis_backup |
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thesis:
quotations.txt
thesis_backup:
quotations.txt |
It is important to include the -r
flag. If you want to copy a directory and you omit this option you will see a message that the directory has been omitted because -r not specified
.
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cp thesis thesis_backup |
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cp: -r not specified; omitting directory 'thesis' |
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RENAMING FILESSuppose that you created a plain-text file in your current directory to contain a list of the statistical tests you will need to do to analyze your data, and named it statstics.txt 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 .
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No. While this would create a file with the correct name, the incorrectly named file still exists in the directory and would need to be deleted. Yes, this would work to rename the file. No, the period(.) indicates where to move the file, but does not provide a new file name; identical file names cannot be created. No, the period(.) indicates where to copy the file, but does not provide a new file name; identical file names cannot be created.
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MOVING AND COPYINGWhat is the output of the closing ls command in the sequence shown below? Code Block |
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/Users/jamie/data |
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$ mkdir recombined
$ mv proteins.dat recombined/
$ cp recombined/proteins.dat ../proteins-saved.dat
$ ls |
proteins-saved.dat recombined
recombined
proteins.dat recombined
proteins-saved.dat
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We start in the /Users/jamie/data directory, and create a new folder called recombined . The second line moves (mv ) the file proteins.dat to the new folder (recombined ). The third line makes a copy of the file we just moved. The tricky part here is where the file was copied to. Recall that .. means ‘go up a level’, so the copied file is now in /Users/jamie . Notice that .. is interpreted with respect to the current working directory, not with respect to the location of the file being copied. So, the only thing that will show using ls (in /Users/jamie/data ) is the recombined folder. No, see explanation above. proteins-saved.dat is located at /Users/jamie Yes No, see explanation above. proteins.dat is located at /Users/jamie/data/recombined No, see explanation above. proteins-saved.dat is located at /Users/jamie
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Removing files and directories
Returning to the shell-lesson-data/exercise-data/writing
directory, let’s tidy up this directory by removing the quotes.txt
file we created. The Unix command we’ll use for this is rm
(short for ‘remove’):
We can confirm the file has gone using ls
:
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ls: cannot access 'quotes.txt': No such file or directory |
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DELETING IS FOREVERThe 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 unlinked 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. |
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USING rm SAFELYWhat happens when we execute rm -i thesis_backup/quotations.txt ? Why would we want this protection when using rm ? |
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rm: remove regular file 'thesis_backup/quotations.txt'? y |
The -i option will prompt before (every) removal (use Y to confirm deletion or N to keep the file). The Unix shell doesn’t have a trash bin, so all the files removed will disappear forever. By using the -i option, we have the chance to check that we are deleting only the files that we want to remove. |
If we try to remove the thesis
directory using rm thesis
, we get an error message:
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rm: cannot remove 'thesis': Is a directory |
This happens because rm
by default only works on files, not directories.
rm
can remove a directory and all its contents if we use the recursive option -r
, and it will do so without any confirmation prompts:
Given that there is no way to retrieve files deleted using the shell, rm -r
should be used with great caution (you might consider adding the interactive option rm -r -i
).
Operations with multiple files and directories
Oftentimes one needs to copy or move several files at once. This can be done by providing a list of individual filenames, or specifying a naming pattern using wildcards. Wildcards are special characters that can be used to represent unknown characters or sets of characters when navigating the Unix file system.
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COPY WITH MULTIPLE FILENAMESFor this exercise, you can test the commands in the shell-lesson-data/exercise-data directory. In the example below, what does cp do when given several filenames and a directory name? Code Block |
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mkdir backup
cp creatures/minotaur.dat creatures/unicorn.dat backup/ |
In the example below, what does cp do when given three or more file names? Code Block |
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cd creatures
ls -F |
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basilisk.dat minotaur.dat unicorn.dat |
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cp minotaur.dat unicorn.dat basilisk.dat |
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If given more than one file name followed by a directory name (i.e. the destination directory must be the last argument), cp copies the files to the named directory. If given three file names, cp throws an error such as the one below, because it is expecting a directory name as the last argument. Code Block |
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cp: target 'basilisk.dat' is not a directory |
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Using wildcards for accessing multiple files at once
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WILDCARDS* is a wildcard, which represents zero or more other characters. Let’s consider the shell-lesson-data/exercise-data/alkanes directory: *.pdb represents ethane.pdb , propane.pdb , and every file that ends with ‘.pdb’. On the other hand, p*.pdb only represents pentane.pdb and propane.pdb , because the ‘p’ at the front can only represent filenames that begin with the letter ‘p’.
? is also a wildcard, but it represents exactly one character. So ?ethane.pdb could represent methane.pdb whereas *ethane.pdb represents both ethane.pdb and methane.pdb .
Wildcards can be used in combination with each other. For example, ???ane.pdb indicates three characters followed by ane.pdb , giving cubane.pdb ethane.pdb octane.pdb . When the shell sees a wildcard, it expands the wildcard to create a list of matching filenames before running the preceding command. As an exception, if a wildcard expression does not match any file, Bash will pass the expression as an argument to the command as it is. For example, typing ls *.pdf in the alkanes directory (which contains only files with names ending with .pdb ) results in an error message that there is no file called *.pdf . However, generally commands like wc and ls see the lists of file names matching these expressions, but not the wildcards themselves. It is the shell, not the other programs, that expands the wildcards. |
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LIST FILENAMES MATCHING A PATTERNWhen run in the alkanes directory, which ls command(s) will produce this output? ethane.pdb methane.pdb
ls *t*ane.pdb
ls *t?ne.*
ls *t??ne.pdb
ls ethane.*
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The solution is 3. shows all files whose names contain zero or more characters (* ) followed by the letter t , then zero or more characters (* ) followed by ane.pdb . This gives ethane.pdb methane.pdb octane.pdb pentane.pdb . shows all files whose names start with zero or more characters (* ) followed by the letter t , then a single character (? ), then ne. followed by zero or more characters (* ). This will give us octane.pdb and pentane.pdb but doesn’t match anything which ends in thane.pdb . fixes the problems of option 2 by matching two characters (?? ) between t and ne . This is the solution. only shows files starting with ethane. .
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MORE ON WILDCARDSSam has a directory containing calibration data, datasets, and descriptions of the datasets: Code Block |
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.
├── 2015-10-23-calibration.txt
├── 2015-10-23-dataset1.txt
├── 2015-10-23-dataset2.txt
├── 2015-10-23-dataset_overview.txt
├── 2015-10-26-calibration.txt
├── 2015-10-26-dataset1.txt
├── 2015-10-26-dataset2.txt
├── 2015-10-26-dataset_overview.txt
├── 2015-11-23-calibration.txt
├── 2015-11-23-dataset1.txt
├── 2015-11-23-dataset2.txt
├── 2015-11-23-dataset_overview.txt
├── backup
│ ├── calibration
│ └── datasets
└── send_to_bob
├── all_datasets_created_on_a_23rd
└── all_november_files |
Before heading off to another field trip, she wants to back up her data and send some datasets to her colleague Bob. Sam uses the following commands to get the job done: Code Block |
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cp *dataset* backup/datasets
cp ____calibration____ backup/calibration
cp 2015-____-____ send_to_bob/all_november_files/
cp ____ send_to_bob/all_datasets_created_on_a_23rd/ |
Help Sam by filling in the blanks. The resulting directory structure should look like this Code Block |
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.
├── 2015-10-23-calibration.txt
├── 2015-10-23-dataset1.txt
├── 2015-10-23-dataset2.txt
├── 2015-10-23-dataset_overview.txt
├── 2015-10-26-calibration.txt
├── 2015-10-26-dataset1.txt
├── 2015-10-26-dataset2.txt
├── 2015-10-26-dataset_overview.txt
├── 2015-11-23-calibration.txt
├── 2015-11-23-dataset1.txt
├── 2015-11-23-dataset2.txt
├── 2015-11-23-dataset_overview.txt
├── backup
│ ├── calibration
│ │ ├── 2015-10-23-calibration.txt
│ │ ├── 2015-10-26-calibration.txt
│ │ └── 2015-11-23-calibration.txt
│ └── datasets
│ ├── 2015-10-23-dataset1.txt
│ ├── 2015-10-23-dataset2.txt
│ ├── 2015-10-23-dataset_overview.txt
│ ├── 2015-10-26-dataset1.txt
│ ├── 2015-10-26-dataset2.txt
│ ├── 2015-10-26-dataset_overview.txt
│ ├── 2015-11-23-dataset1.txt
│ ├── 2015-11-23-dataset2.txt
│ └── 2015-11-23-dataset_overview.txt
└── send_to_bob
├── all_datasets_created_on_a_23rd
│ ├── 2015-10-23-dataset1.txt
│ ├── 2015-10-23-dataset2.txt
│ ├── 2015-10-23-dataset_overview.txt
│ ├── 2015-11-23-dataset1.txt
│ ├── 2015-11-23-dataset2.txt
│ └── 2015-11-23-dataset_overview.txt
└── all_november_files
├── 2015-11-23-calibration.txt
├── 2015-11-23-dataset1.txt
├── 2015-11-23-dataset2.txt
└── 2015-11-23-dataset_overview.txt |
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cp *calibration.txt backup/calibration
cp 2015-11-* send_to_bob/all_november_files/
cp *-23-dataset* send_to_bob/all_datasets_created_on_a_23rd/ |
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ORGANIZING DIRECTORIES AND FILESJamie is working on a project, and she sees that her files aren’t very well organized: Code Block |
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analyzed/ fructose.dat raw/ sucrose.dat |
The fructose.dat and sucrose.dat files 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? Code Block |
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fructose.dat sucrose.dat |
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mv *.dat analyzed |
Jamie needs to move her files fructose.dat and sucrose.dat to the analyzed directory. The shell will expand *.dat to match all .dat files in the current directory. The mv command then moves the list of .dat files to the ‘analyzed’ directory. |
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REPRODUCE A FOLDER STRUCTUREYou’re starting a new experiment and would like to duplicate the directory structure from your previous experiment so you can add new data. Assume that the previous experiment is in a folder called 2016-05-18 , which contains a data folder that in turn contains folders named raw and processed that contain data files. The goal is to copy the folder structure of the 2016-05-18 folder into a folder called 2016-05-20 so that your final directory structure looks like this: Code Block |
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2016-05-20/
└── data
├── processed
└── raw |
Which of the following set of commands would achieve this objective? What would the other commands do? Code Block |
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$ mkdir 2016-05-20
$ mkdir 2016-05-20/data
$ mkdir 2016-05-20/data/processed
$ mkdir 2016-05-20/data/raw |
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$ mkdir 2016-05-20
$ cd 2016-05-20
$ mkdir data
$ cd data
$ mkdir raw processed |
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$ mkdir 2016-05-20/data/raw
$ mkdir 2016-05-20/data/processed |
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$ mkdir -p 2016-05-20/data/raw
$ mkdir -p 2016-05-20/data/processed |
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$ mkdir 2016-05-20
$ cd 2016-05-20
$ mkdir data
$ mkdir raw processed |
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The first two sets of commands achieve this objective. The first set uses relative paths to create the top-level directory before the subdirectories. The third set of commands will give an error because the default behavior of mkdir won’t create a subdirectory of a non-existent directory: the intermediate level folders must be created first. The fourth set of commands achieve this objective. Remember, the -p option, followed by a path of one or more directories, will cause mkdir to create any intermediate subdirectories as required. The final set of commands generates the ‘raw’ and ‘processed’ directories at the same level as the ‘data’ directory. |
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KEYPOINTScp [old] [new] copies a file.
mkdir [path] creates a new directory.
mv [old] [new] moves (renames) a file or directory.
rm [path] removes (deletes) a file.
* matches zero or more characters in a filename, so *.txt matches all files ending in .txt .
? matches any single character in a filename, so ?.txt matches a.txt but not any.txt .
Use of the Control key may be described in many ways, including Ctrl-X , Control-X , and ^X . The shell does not have a trash bin: once something is deleted, it’s really gone. Most files’ names are something.extension . The extension isn’t required, and doesn’t guarantee anything, but is normally used to indicate the type of data in the file. Depending on the type of work you do, you may need a more powerful text editor than Nano.
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