Embedded Files
Topics:
Files in Linux
Directories
Directory Tree Diagram
Root Directory
Home Directory
Directory Path
Commands
pwd and cd
ls and directories
mkdir and rmdir
cp and Directories
mv and Directories
which and whereis
Files in Linux
The Linux philosophy is “everything is a file”
The term “file” not only means a file of data (the typical meaning), it can also refer to an input device (such as a scanner), an output device (such as the monitor), a hardware component (such as the hard drive), or a process (such as the shell that you work with)
Linux divides files into 7 different types:
1. regular file: a file of data. Data can be text (human readable) or binary (machine readable)
2. directory: a file that can “contain” other files (equivalent to folders in Windows)
3. character special file: IO device that processes one character at a time, such as a printer
4. block special file: IO device that processes a block of characters at a time, such as a hard disk
5. symbolic link: a file that holds the address of another file
6. FIFO: a file used for inter-process communication
7. socket: a file used for network communication
Directories
Directories help you organize files by providing ways to group similar files together
In Linux, files are grouped into directories (which themselves are files), and directories are grouped under other directories, in “tree” form called a directory tree or directory hierarchy
Each file in the hierarchy is called a node
The top node is called root
Except for root, each node can have
1 node above it, called its parent node
0 or more nodes below it, called its child nodes
A parent directory can have directory child nodes, called subdirectories
Directory Tree Diagram
In this sample directory tree:
There are 9 files
Each file is a node
One root node
DirectoryC is the child node of root, and is the parent node of a regular file
DirectoryD is the subdirectory of DirectoryB
Root Directory
There is only one root node for every directory hierarchy
The actual name you type in for root is /
Some common subdirectories under root are
bin: (for binary) contains general Linux utilities, in binary format
sbin: (for system binary) contains utilities for system administration
etc: contains configuration files for the system
usr: (for user) contains applications for the users
lib: (for library) shared libraries
var: (for variable) contains data files that change when the system is running
tmp: (for temporary) contains temporary files
dev: (for device) contains files for hardware devices
mnt: (for mount) contains mount points for storage devices
home: contains home directories of users
Home Directory
Every user is assigned a unique directory to store his / her files. This directory is called the home directory
It has the same name as your log in name
You cannot change your home directory name or its location in the system
When you first log in the system, you are at the home directory
Often you will not be at the home directory. Instead you will move to a different directory, depending on the task you are doing. The directory where you are working is called the current directory or the working directory
Directory Path
Since the Linux directory tree is a huge hierarchy of files, it is important to know the path to a file in order to access it
The path of a file is the location of the file in the directory tree
A path is formed by
listing node names that are connected to each other in the tree structure
separate node names with / (not the same as root)
2 types of paths: absolute path and relative path
Absolute path
Shows the location of a file, starting from root /
The absolute path of a file will not change unless the file is moved to another place in the hierarchy
Relative path
Shows the location of a file, starting from your current directory
Since the relative path is relative to your current directory, the relative path of a file will change if you change your current directory
Assume your home directory is ImaStudent:
All commands that accept a filename as an argument will accept a filename with a path
When a filename with no path is the argument, the file needs to be in the current directory or the shell will not be able to find it
When a filename with a path is the argument, the file needs wherever the path indicates
Examples:
ls fileA will list fileA in the current directory
ls /labs/fileA will list fileA that is in the labs directory which is under root
cp fileA fileB will make a copy of fileA in the current directory and store it as fileB in the current directory
cp fileA /files/fileB will make a copy of fileA in the current directory and store it as fileB in the files directory, which is under root directory
pwd and cd
pwd: (for print working directory) shows the absolute path of where you are in the directory tree
cd: (for change directory) moves you to another directory
Common format: cd path
where path can be:
Nothing: moves you to your home directory
Absolute path: make sure it starts with / (root)
Relative path: make sure the first node in the path is connected to your current directory
To go to a subdirectory: type the name of the subdirectory
To go to a parent directory: type ..
To go to the current directory: type .
Path with special symbols:
~ your home directory
~userID home directory of user userID
ls and Directories
Recall:
ls will list filenames in the current directory
ls filename will echo filename if file exists and is a regular file
If filename is the name of a directory, then ls will list filenames under that directory
To see the file type of a file:
Use the long listing: ls –l
The first character in the mode column will tell you the file type: d for directory, l for link, - for regular file
Use: ls –F
The filenames will be listed with an additional symbol at the end: / for directory, @ for link, * for executable regular file, nothing for text file (which is also a regular file)
mkdir and rmdir
mkdir: (for make directory) creates a new directory in the current directory, or under a different directory if a path is given
Common format: mkdir directory_name
When first created, the directory is an empty directory (no files in it, except 2 hidden files . and ..)
rmdir: (for remove directory) deletes an empty directory
If the directory is not empty, you must delete all files in it first
Common format: rmdir directory_name
Alternatively, to remove a non-empty directory, use rm –r directory_name where -r is for recursive
Removes the directory and recursively go down all its subdirectories and remove all the files under them
Caution: this can remove a large number of files, make sure you don’t run this command ‘by accident’
cp and Directories
Recall that cp will copy the source file to the destination file. Now we discuss all the combinations of cp with regular files and with directories
File below means regular file, Dir below means directory
Copying a source regular file
cp existingFile nonExistingFile new nonExistingFile is created
cp existingFile1 existingFile2 existingFile2 is overwritten
cp existingFile nonExistingDir new regular file created with the name of nonExistingDir
cp existingFile existingDir new file called existingFile created under existingDir
Copying a source directory (need to use –r option, for recursively copy, all files and subdirectories will also get copied)
cp –r existingDir nonExistingDir new nonExistingDir is created
cp –r existingDir1 existingDir2 existingDir1 is copied and put under existingDir2
cp –r existingDir nonExistingFile new directory called nonExistingFile is created
cp –r existingDir existingFile not possible
mv and Directories
Recall that mv will move the source file to the destination file, and the source file will no longer exist. Now we discuss all the combinations of mv with regular files and with directories
File below means regular file, Dir below means directory
Move a source regular file
mv existingFile nonExistingFile new nonExistingFile is created
mv existingFile1 existingFile2 existingFile2 is overwritten
mv existingFile nonExistingDir new regular file created with the name of nonExistingDir
mv existingFile existingDir new file called existingFile created under existingDirectory
Moving a source directory (don’t need option, all files and subdirectories will move)
mv existingDir nonExistingDir new nonExistingDir is created
mv existingDir1 existingDir2 existingDir1 moves under existingDir2
mv existingDir nonExistingFile new directory called nonExistingFile is created
mv existingDir existingFile not possible
which and whereis
These commands give the path (location) of a particular utility. They only accept a utility name as an argument
which utility_name
shows the actual utility that runs when utlity_name is typed on the command line
Example: [testuser@abc ~]$ which vi
alias vi='vim'
/usr/bin/vim
whereis utility_name
shows the location of the utility in the system
Example: [testuser@abc ~]$ whereis vi
vi: /bin/vi /usr/share/man/man1/vi.1.gz /usr/share/man/man1p/vi.1p.gz
If you know the location of a utility and you want to run it, type the absolute path of the utility on the command line
Example: To run vi instead of vim: [testuser@abc ~]$ /bin/vi filename
The absolute path of your home directory is /home/student/ImaStudent
From the root directory, you can use a relative path to the distribution directory by traversing down to home, then down to distribution. The relative path from root is: home/distribution
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