Files & Directories

In linux, everything is a file or directory. All files and directories have a path. There is a relative and a full path, with relative being a path relative to the current working directory.

To see your current working directory, run the pwd (Print Working Directory) command.

$ pwd
/home/sysadmin

Listing Files and Directories

The ls (LiSt) command lists the contents of a directory. If no arguments are specified, it lists the contents of the current directory.

$ ls
development
Documents
Downloads
Pictures

$ ls Pictures
picture-of-a-cat.png
picture-of-a-dog.jpg

Files that begin with a . are "hidden" files, and do not normally appear the output of an ls command. To show all files, use the -a (All) flag.

$ ls -a
.bash_history
.bash_logout
.bash_profile
.bashrc
.profile
.vimrc
development
Documents
Downloads
Pictures

Changing Your Working Directory

The cd command changes your working directory to the path you specify. Paths can be relative or absolute.

Absolute Paths

Absolute paths are paths that begin from / (root).

$ cd /home/sysadmin/Documents
$ # or
$ cd ~/Documents

Note: The ~ (tilde) character is a shortcut for the current user's home directory.

Relative Paths

Relative paths are paths relative to the current working directory.

The simplest relative path is a child directory of the current working directory.

$ ls
Documents
Pictures

$ cd Documents
$ ls
Guide.pdf
Resources.txt

. is the current directory.

$ pwd 
/home/sysadmin
$ cd .
$ pwd
/home/sysadmin

.. is the parent directory.

$ pwd 
/home/sysadmin/Pictures
$ cd ..
$ pwd
/home/sysadmin

And more complex...

$ pwd
/home/sysadmin/Pictures
$ cd ../Documents
$ pwd
/home/sysadmin/Documents

Copying and Moving Files & Directories

Copying

Use the cp (CoPy) command to copy files and directories.

$ cp <source> <destination>

To copy a directory AND its contents, use the -r (Recursive) flag.

$ cp -r <source directory> <destination directory>

Moving

Moving files and directories works much the same with the mv (MoVe) command.

$ mv <source> <destination>

You can also use the mv command to rename a file or directory

$ mv <oldname> <newname>

Links

A link works like a file to point from one place to another. There are two types of links:

A hard link is a file that points to the inode of another file. If this "pointed-to" file is deleted, the data persists until all hard links are removed (a normal file acts as a hard link to itself). A hard link can only be created for files, not directories.

Create a hard link with the ln (LiNk) command.

ln <source> <destination>

$ cat srcFile
hello i am a file.
$ ln srcFile hardLink
$ rm srcFile
$ cat hardLink
hello i am a file.

In the permissions section, we look at the ls -l command. We can see the number of hard links to a file in the output. 

$ ls -l
-rw-rw-r--  1 sysadmin  users  0    Dec  1  2021    srcFile
-rw-r--r--  1 sysadmin  users  584  Mar  10 2022    script.sh

The number before sysadmin is the number of hard links.

$ ln srcFile hardLink
$ ls -l
-rw-rw-r--  2 sysadmin  users  0    Dec  1  2021    hardlink
-rw-rw-r--  2 sysadmin  users  0    Dec  1  2021    srcFile
-rw-r--r--  1 sysadmin  users  584  Mar  10 2022    script.sh

As we can see here, after adding a hard link, the number of hard links increases for the source file, and the number is reflected in the hard link too.

A symbolic link (symlink for short) is a file that points to another file or directory's path. If the "pointed-to" file or directory is deleted, the link is no longer valid, and points to a non-existent file or directory.

The -s (Soft) flag specifies a symbolic link.

To create a link called newLink to a file called srcFile, run the following command:

$ ln -sf srcFile newLink

$ cat srcFile
this is the source file
$ ln -sf srcFile newLink
$ cat newLink
this is the source file

The cat (conCATenate) command allows you to read the contents of a file.