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--- wiki:cli:creating_things [2015/09/05 20:25] – Add home to path. jensv
+++ wiki:cli:creating_things [2022/07/21 06:59] (current) – external edit 127.0.0.1
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+====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 home directory,
+''/home/users/jens'',
+and use ''ls -F'' to see what it contains:
+    $ pwd
+    /home/users/jens
+    $ ls -F
+    desktop.examples   school/
+Let's create a new directory called ''thesis'' using the command ''mkdir theis''
+(which has no output):
+    $ mkdir thesis
+As you might (or might not) guess from its name,
+''mkdir'' means "make directory".
+Since ''thesis'' is a relative path
+(i.e., doesn't have a leading slash),
+the new directory is made below the current working directory:
+    $ ls -F
+    desktop.examples   school/     thesis/
+However, there's nothing in it yet:
+    $ ls -F thesis
+Let's change our working directory to ''thesis'' using ''cd'',
+then run a text editor called Nano to create a file called ''draft.txt'':
+    $ cd thesis
+    $ nano draft.txt
+> 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 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](http://www.gnu.org/software/emacs/) or
+> [Vim](http://www.vim.org/) (both of which are completely unintuitive,
+> even by Unix standards), or a graphical editor such as
+> [Gedit](http://projects.gnome.org/gedit/). On Windows, you may wish to
+> use [Notepad++](http://notepad-plus-plus.org/).
+>
+> 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,
+then use Control-O to write our data to disk:
+Once our file is saved,
+we can use Control-X to quit the editor and return to the shell.
+(Unix documentation often uses the shorthand ''^A'' to mean "control-A".)
+''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'':
+    $ ls
+    draft.txt
+Let's tidy up by running ''rm draft.txt'':
+    $ rm draft.txt
+This command removes files ("rm" is short for "remove").
+If we run ''ls'' again,
+its output is empty once more,
+which tells us that our file is gone:
+    $ ls
+> Deleting Is Forever
+>
+> Unix doesn't have a trash bin: 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 ''/home/users/jens'' using ''cd ..'':
+    $ pwd
+    /home/users/jens/thesis
+    $ nano draft.txt
+    $ ls
+    draft.txt
+    $ cd ..
+If we try to remove the entire ''thesis'' directory using ''rm thesis'',
+we get an error message:
+    $ rm thesis
+    rm: cannot remove thesis: Is a directory
+This happens because ''rm'' only works on files, not directories.
+The right command is ''rmdir'',
+which is short for "remove directory".
+It doesn't work yet either, though,
+because the directory we're trying to remove isn't empty:
+    $ rmdir thesis
+    rmdir: failed to remove 'thesis': Directory not empty
+This little safety feature can save you a lot of grief,
+particularly if you are a bad typist.
+To really get rid of ''thesis'' we must first delete the file ''draft.txt'':
+    $ rm thesis/draft.txt
+The directory is now empty, so ''rmdir'' can delete it:
+    $ rmdir thesis
+> With Great Power Comes Great Responsibility
+>
+> Removing the files in a directory just so that we can remove the
+> directory quickly becomes tedious. Instead, we can use ''rm'' with the
+> ''-r'' flag (which stands for "recursive"):
+>
+>
+> ''$ rm -r thesis''
+>
+>
+> This removes everything in the directory, then the directory itself. If
+> the directory contains sub-directories, ''rm -r'' does the same thing to
+> them, and so on. It's very handy, but can do a lot of damage if used
+> without care.
+Let's create that directory and file one more time.
+(Note that this time we're running ''nano'' with the path ''thesis/draft.txt'',
+rather than going into the ''thesis'' directory and running ''nano'' on ''draft.txt'' there.)
+    $ pwd
+    /home/users/jens
+    $ mkdir thesis
+    $ nano thesis/draft.txt
+    $ ls thesis
+    draft.txt
+''draft.txt'' isn't a particularly informative name,
+so let's change the file's name using ''mv'',
+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,
+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'':
+    $ ls thesis
+    quotes.txt
+Just for the sake of inconsistency,
+''mv'' also works on directories; there is no separate ''mvdir'' command.
+Let's move ''quotes.txt'' into the current working directory.
+We use ''mv'' once again,
+but this time we'll just use the name of a directory as the second parameter
+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.
+    $ 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
+Further,
+''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
+    quotes.txt
+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 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
+    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 ''ls'' again.
+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:
+    $ ls quotes.txt thesis/quotations.txt
+    ls: cannot access quotes.txt: No such file or directory
+    thesis/quotations.txt
+> Another Useful Abbreviation
+>
+> The shell interprets the character ''~'' (tilde) at the start of a path to
+> mean "the current user's home directory". For example, if Jens' home
+> directory is ''/home/users/jens'', then ''~/data'' is equivalent to
+> ''/home/users/jens/data''. This only works if it is the first character in the
+> path: ''here/there/~/elsewhere'' is *not* ''/home/users/jens/elsewhere''.
+====Key Points====
+  *Unix documentation uses '^A' to mean "control-A".
+  *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.