What is a shell?

• Linux shell is a program that allows text-based interaction between the user and the computer

Types of shell in Linux

Linux Commands

• Linux command consists of program name followed by the option and arguments.
• For ex.

cat -n myfile

# program name: cat
# option: -n
# argument: myfile

Home directory

• The home directory is a directory that stores user-specific data.
• this data can be of any type
• for ex. If there is a user named john, then john's data like images, documents, downloads, etc. data will reside in /home/john/ location

How to know the Home directory

echo $HOME
# This command will read from the environment variable $HOME

echo ~
# This command will expand the tilde symbol to the given user's home directory path

Directory Management

How to know your current path

• To know the current path, we use the command pwd, which stands for Present working directory

pwd 

How to create & remove directories

• mkdir is a command that is used to create a directory
• rmdir is a command that is used to delete an empty directory
• example

# to create a directory
mkdir test_directory

# to create multiple directories
mkdir test1 test2 test3

# to delete a directory
rmdir test_directory

# to remove multiple directories
rmdir test1 test2 test3

How to list the content of a folder

• to list the content of a directory we use the ls command

# to list the content of a directory
ls 

How to create a chain of directories

• in order to perform this we use the "-p" parameter with mkdir command
• Example

# We want to create 4 directories each inside of it's parent directory
mkdir -p a/b/c/d

How to navigate through directories

• To switch directories we use cd command

# Changing to the parent directory
cd ../

# Changing to the home directory
cd /home/user1

How to navigate folder directory in Linux

• there are two types of path notation in Linux
• 1. Relative Path
• 2. Absolute Path

Relative path

• relative path is defined with respect to the current directory
• "." represents the current working folder
• ".." represents the parent directory
• For example

# to change to the parent directory for the current directory
cd ../

# to run a file/script present in the current directory
bash ./example.sh

Absolute path

• absolute paths are defined with respect to the root "/" location
• for example

# navigating to the user1 document folder
cd /home/user1/documents

PUSHD & POPD

• pushd and popd commands are used to manage the directory stack.
• Example

# we created 3 directories
mkdir -p a/b/c

# now we navigate to c directory using pushd command, by pushing it's path to directory stack
pushd a/b/c

# this command will take us to the given c directory and we can create a file here
echo "hello world" > test_file.txt

# to navigate to the previous path we can use popd command
# this will bring us to the parent directory
popd