103.1 Work on the Command Line

Mastering Command Line Basics: LPIC-1 Exam Objective 103.1 #

As you prepare for the LPIC-1 certification, mastering the command line is essential. This tutorial covers key aspects of interacting with shells and commands using the command line, focusing on the Bash shell. We’ll delve into single shell commands, shell environment modification, command history, and invoking commands inside and outside the defined path.

Single Shell Commands and One-Line Command Sequences #

Basic Shell Commands #

echo: Print text to the terminal.
```
echo "Hello, World!"
```
Output:
```
Hello, World!
```
pwd: Print the current working directory.
```
pwd
```
Output:
```
/home/user
```

uname: Display system information.

uname -a

Output:

Linux hostname 5.4.0-74-generic #83-Ubuntu SMP Mon May 10 19:18:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

One-Line Command Sequences #

Combine multiple commands using the ; separator.

mkdir test_dir; cd test_dir; touch file1 file2; ls

This sequence creates a directory, navigates into it, creates two files, and lists them.

Shell Environment #

Defining, Referencing, and Exporting Environment Variables #

Defining a variable:
```
MY_VAR="Hello"
```
Referencing a variable:
```
echo $MY_VAR
```
Output:
```
Hello
```
Exporting a variable:
```
export MY_VAR
```
Using env to view environment variables:
```
env | grep MY_VAR
```
Output:
```
MY_VAR=Hello
```
Unsetting a variable:
```
unset MY_VAR
```

Command History #

Viewing command history:
```
history
```
Re-running a command from history:
```
!42
```
This runs the command numbered 42 in the history.
Editing history with history -c:
```
history -c
```
This clears the command history.

Invoking Commands #

Inside the Defined Path #

Commands within the system’s PATH can be executed directly.

Using which to locate executables:
```
which ls
```
Output:
```
/bin/ls
```

Using type to display command type:

type ls

Output:

ls is aliased to `ls --color=auto`

Outside the Defined Path #

To run a script not in the PATH, specify its path.

Running a script from the current directory:
```
./script.sh
```

Quoting in Shell #

Quoting controls the interpretation of special characters.

Double quotes ("):

echo "The value of HOME is $HOME"

Output:

The value of HOME is /home/user

Single quotes ('):

echo 'The value of HOME is $HOME'

Output:

The value of HOME is $HOME

Backslash (\) for escaping:
```
echo "A quote: \""
```
Output:
```
A quote: "
```

Summary #

This tutorial covered the essentials of working on the command line with Bash, including single shell commands, modifying the shell environment, using command history, and invoking commands inside and outside the defined path. Mastering these basics is crucial for success in the LPIC-1 exam and for efficient daily use of the Linux command line. Happy learning!