Mastering Shell Commands On Linux

By Urko Galen

This book is a practical guide to Linux commands for beginner and intermediate users.

 

It focuses on essential skills for file and process management, providing step-by-step instructions for manipulating files and directories, managing running processes, and understanding basic terminal commands.

 

The explanations are clear and accompanied by concrete examples for better understanding.

Whether you are a computer science student or a user looking to improve your file management skills, this book is an indispensable tool for learning Linux commands and increasing your efficiency

• Language: English
• Publisher: Urko GAlen
• Release date: Mar 11, 2023
• ISBN: 9798215013786

Book preview

Urko Galen

Mastering Shell Commands On Linux

Introduction

This book is intended for beginners and advanced users who wish to learn and deepen their shell skills under Linux.

It is accessible even if you have no programming or command line experience. We have included practical examples to better understand each command and its options.

Thank you for accompanying us on this journey to become experts in Linux shell commands.

Contents

1      man apropos help: command help

1.1      Description

1.2      Example

2      ls: list files and folders in a directory

2.1      Description

2.2      Example

3      cp: copy files or folders

3.1      Description

3.2      Example

4      mv: moves a file or directory to another location

4.1      Description

4.2      Example

5      rm: delete a file

5.1      Description

5.2      Example

6      ln: create a symbolic link to a file or directory

6.1      Description

6.2      Example

7      cd: change directory

7.1      Description

7.2      Example

8      basename: change directory

8.1      Description

8.2      Example

9      dirname: display the path of the current directory

9.1      Description

9.2      Example

10      mkdir: create a new directory

10.1      Description

10.2      Example

11      rmdir: delete an empty directory

11.1      Description

11.2      Example

12      pwd: display the path of the current directory

12.1      Description

12.2      Example

13      touch: create a new file

13.1      Description

13.2      Example

14      cat: print the contents of one or more files to standard output

14.1      Description

14.2      Example

15      less: view the contents of a file

15.1      Description

15.2      Example

16      head and tail: Displaying a file

16.1      Description

16.2      Example

17      | (pipe)

17.1      Description

17.2      Example

18      grep: search for a specified pattern in a file or standard output

18.1      Description

18.2      Example

18.3      Exercise - corrected

19      cut: cut and select columns from a file or standard output

19.1      Description

19.2      Example

19.3      Exercise - corrected

20      Paste: file merge

20.1      Description

20.2      Example

21      tr: convert characters

21.1      Description

21.2      Example

22      sort: sort the lines of a file or standard output

22.1      Description

22.2      Example

22.3      Exercise – corrected

23      uniq: remove duplicate lines

23.1      Description

23.2      Example

24      tee: redirect output to a file

24.1      Description

24.2      Example

25      sed: changes to a file or standard output

25.1      Description

25.2      Example

25.3      Exercise – corrected

26      df: Check disk space size

26.1      Description

26.2      Example

26.3      Exercise – corrected

27      du: Check directory size

27.1      Description

27.2      Example

27.3      Exercise – corrected

28      uname: System Information

28.1      Description

28.2      Example

29      who – User information

29.1      Description

29.2      Example

30      crontab: Task scheduler

30.1      Description

30.2      Example

31      nohup: Run script in background

31.1      Description

31.2      Example

32      lsof: list the files used by the system

32.1      Description

32.2      Example

32.3      Exercise – corrected

33      history: list the history of commands

33.1      Description

33.2      Example

34      echo: On-screen display

34.1      Description

34.2      Example

35      tar archive files and/or directories

35.1      Description

35.2      Example

35.3      Exercise – corrected

36      gzip and gunzip: Archive/Unarchive zip

36.1      Description

36.2      Example

37      zcat: display the contents of a compressed file

37.1      Description

37.2      Example

38      chmod: change permissions of a file or directory

38.1      Description

38.2      Example

39      awk: word processing tool

39.1      Description

39.2      Example

39.3      Exercise – corrected

40      diff: compare files

40.1      Description

40.2      Example

41      chown: Change owner or group of a file/directory

41.1      Description

41.2      Example

42      alias: create an alias for a command

42.1      Description

42.2      Example

43      free: RAM

43.1      Description

43.2      Example

43.3      Exercise – corrected

44      kill: Kills a running process

44.1      Description

44.2      Example

45      ps: Displays the list of running processes

45.1      Description

45.2      Example

45.3      Exercise - corrected

46      top: Shows running processes

46.1      Description

46.2      Example

46.3      Exercise - corrected

47      find: search for files and directories

47.1      Description

47.2      Example

47.3      Exercise - corrected

48      xargs: process the output of a command

48.1      Description

48.2      Example

49      locate : locate a file

49.1      Description

49.2      Example

50      wich : locate a binary

50.1      Description

50.2      Example

51      type : command type

51.1      Description

51.2      Example

52      whereis locate file

52.1      Description

52.2      Example

53      Conditions

53.1      Description

53.2      Example

54      For and while loop

54.1      Description

54.2      Example

54.3      Exercise - corrected

55      regular expression

55.1      Description

55.2      Example

56      Redirects

56.1      Redirect standard output

56.2      Redirect standard input

56.3      Error output redirection

56.4      Combination of redirects

57      Mail sending

57.1      Description

57.2      Example

58      Date: Show date

58.1      Description

59      Functions

59.1      Description

60      Script: set of commands

60.1      Description

60.2      Example

61      The variables :

61.1      Description

61.2      Example

62      wc: count the number of rows

62.1      Description

62.2      Example

63      Ping: test network connectivity

63.1      Description

63.2      Example

64      Join: file join

64.1      Description

64.2      Example

65      copyright notice

The help command is used to display built-in help for a specific shell command. It provides information about the command's syntax, available options, and a brief description of how it works. This command is especially useful for beginners who want to learn more about a specific command.

The man command, on the other hand, is a very powerful documentation tool that can display man pages for various Linux commands. These pages provide detailed information about using a command, including examples, available options, and syntax information. It is also possible to search for information about a specific command using the man -k command.

Finally, the apropos command allows you to search for commands based on their functionality or description. It uses man pages to find matching commands based on specific keywords. This command is very useful when you know the functionality you want to perform, but you don't know the exact command to use.

In sum, the help command provides built-in help for a specific command, the man command provides extensive documentation for various Linux commands, and the apropos command helps to find commands based on their functionality or description.

Here are usage examples for the help, man and apropos commands with partial results

Help command:

Suppose you want to view help for the Bash shell builtin cd command. You can enter the following command in the terminal:

help cd

This command will display information about the cd command syntax, available options, and usage examples. Here is a partial example result:

cd [-L|[-P [-e]] [-@]] [dir]

Change the shell working directory.

Change the current directory to DIR. The default DIR is the value of the HOME shell variable.

Options:

-L       force symbolic links to be followed: resolve symbolic links in DIR after processing instances of `..'

-P       use the physical directory structure without following symbolic links: resolve symbolic links in DIR before processing instances of `..'

-e       if the -P option is supplied, and the current working directory cannot be determined successfully, exit with a non-zero status

…

man command:

Suppose you want to view the manual for the ls command which is used to list the contents of a directory. You can enter the following command in the terminal:

man ls

This command will display detailed information about the ls command, including syntax, available options, and usage examples. Here is a partial example result:

LS(1) User Commands LS(1)

NAME

ls - list directory contents

SYNOPSIS

ls [OPTION]... [FILE]...

DESCRIPTION

List information about the FILEs (the current directory by default).

Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

Mandatory arguments to long options are mandatory for short options too.

-a, --all

do not ignore entries starting with .

-A, --almost-all

do not list implied . and ..

--author

with -l, print the author of each file

-b, --escape

print C-style escapes for nongraphic characters

...

apropos command:

Suppose you are looking for a command that allows you to find files on your system. You can enter the following command in the terminal:

apropos find

This command will display a list of all commands and programs that contain the keyword find in their name or description. Here is a partial example result:

find (1) - search for files in a directory hierarchy

findmnt (8) - find a filesystem

fusermount (1) - unmount FUSE filesystems

gappletviewer-4.8 (1) - Find and execute the appletviewer script

gfind4 (1) - find files by name or content

…

The ls command lists the files and folders in a directory. It displays the contents of a directory (file names, symbolic link folders). It is used with several options to display more details about files and/or folders.

ls

This command without options displays the list of files and folders in the current directory.

-------------------------------

ls -lh

Display the list of files and folders in the current directory with additional information, using an alternate display format.

-------------------------------

ls -l

The -l option displays a detailed list of files and folders, including ownership information, size, date modified, etc.

ls -al

The -a and -l options combined display a detailed list including hidden files as well.

-------------------------------

ls ~/Documents

This command displays the list of files and folders in the Documents directory which is in your home directory.

-------------------------------

ls -R /etc

The -R option displays a recursive list of all files and folders under /etc.

The cp command is used to copy files and/or directories from one location to another.

The syntax of cp is:

cp [options] source destination

The most used options:

• -f as force: replaces the destination file without asking for confirmation, even if it is a symbolic link to a directory.

• -i like interactive: ask for confirmation before overwriting an existing file.

• -a:archive: recursively copies all files and subdirectories, as well as symbolic links, permissions, timestamps, etc.

• -r as recursive: recursively copies all files and subdirectories.

• -v like verbose: displays detailed information about the copy operations performed.

cp file1.txt file2.txt

This command will copy the contents of file file1.txt into file2.txt. The new file will, in this example, be created in the same directory as the source file.

If the file file2.txt already exists, its content will be replaced by the file file1.txt.

Without any options on the command, it only copies the contents of the file and not the attributes of the file such as permissions, ownership, modification date, etc.

-------------------------------

If you want to copy the file to another directory, specify the full path of the new file: see example below

cp file.txt /home/user/documents/newfile.txt

If you want to keep the attributes of the source file when copying, use the -p option with the cp command, like this

cp -p file1.txt file2.txt

This will copy file file1.txt