1. Manipulating files and directories

To work with files and directories we can use these commands:

cp - Copy files and directories
mv - Move/rename files and directories
mkdir - Create directories
rm - Remove files and directories
ln - Create hard and symbolic links

Let's use them in some examples.

Creating directories:

cd

mkdir playground

cd playground

mkdir dir1 dir2

ls -l

Copying files:
```
cp /etc/passwd .
```
```
ls -l
```
Notice that . is the current working directory.
```
cp -v /etc/passwd .
```
The option -v makes the command verbose.
```
cp -i /etc/passwd .
```
The option -i makes the command interactive. This means that it asks you first, before doing any potentially destructive actions. Press y or n to continue.

Moving and renaming files:

mv passwd fun

ls -l

mv fun dir1

ls -l

ls -l dir1

mv dir1/fun dir2

ls -l dir1

ls -l dir2

mv dir2/fun .

tree

mv fun dir1

mv dir1 dir2

tree

ls -l dir2/dir1

mv dir2/dir1 .

mv dir1/fun .

tree

Creating hard links:
```
ln fun fun-hard
```
```
ln fun dir1/fun-hard
```
```
ln fun dir2/fun-hard
```
```
ls -lR
```
Notice that the second field in the listing of fun and fun-hard is 4, which shows the number of the links for the file. Hard links are like different names for the same file content.

To make sure that all four of them are the same file, let's try the option -i:
```
ls -lRi
```
You may notice that the number on the first column is the same for all the files. This is called the inode number of a file, and can be thought as the address where the file is located. Since it is the same for all the files, this shows that they are actually the same file.
Creating symbolic links:
```
ln -s fun fun-sym
```
```
ls -l
```
Symbolic links are a special type of file that contains a text pointer to the target file or directory. They were created to overcome two disadvantages of hard links:
1. hard links cannot span physical devices
2. hard links cannot reference directories, only files
```
ln -s ../fun dir1/fun-sym
```
```
ln -s ../fun dir2/fun-sym
```
```
tree
```
These two examples might seem a bit difficult to understand what is going on. But remember that when we create a symbolic link, we are creating a text description of where the target file is, relative to the symbolic link.

We can also use absolute file names when creating symbolic links:
```
ln -sf /home/user1/playground/fun dir1/fun-sym
```
```
ls -l dir1/
```
However, in most cases, using relative pathnames is more desirable, because it allows a directory tree containing symbolic links and their referenced files to be renamed and/or moved without breaking the links.

In addition to regular files, symbolic links can also reference directories:
```
ln -s dir1 dir1-sym
```
```
ls -l
```
Removing files and directories.

Let's clean up the playground a little bit. First let's delete one of the hard links:
```
rm fun-hard
```
```
ls -l
```
Notice that the link count for fun is reduced from 4 to 3 (as indicated in the second field of the directory listing).
```
rm -i fun
```
Press y
```
ls -l
```
```
less fun-sym
```
The symbolic link now is broken.
```
rm fun-sym dir1-sym
```
```
ls -l
```
When we remove a symbolic link the target is not touched.
```
rm -r dir1/
```
```
cd ..
```
```
rm -rf playground/
```

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