This document provides an introduction to Linux and summarizes key topics including: 1. The history and development of Linux including influences from Multics and Unix as well as contributions from developers like Ken Thompson, Dennis Ritchie, and others. 2. Important related operating systems and distributions like BSD, Debian, Ubuntu, and others that helped shape Linux. 3. Core Linux concepts like the Unix philosophy, shells, files/file systems, users/permissions, and commands.

1. Introduction to Linux
2017-09-09 15:21
xuqiang@gridsum.com

2. Agenda
• Multics/Unix
• BSD
• Unix philosophy
• GNU/Linux/Linux distribution
• Debian on VM
• Oracle VirtualBox/VMware Player
• APT: Advanced Package Tool
• Shell/SSH/Putty/Xshell
• File/File System
• Process
• User/Group
• File System Permissions
• Signal
• Standard IO/Pipeline
• Vim: God of the text editors / Emacs: a text editor of the Gods

3. Multics/Unix
• Multics
• an influential early time-sharing operating system
• MIT, GE, Bell Labs
• Unix
• Ken Thompson
• The designer and implementer of the original Unix
• Since 2006, Thompson has worked at Google, where he co-invented the Go programming language.
• C and Unix
• Dennis Ritchie: the creator of the C programming language
• In 1972, Unix was rewritten in the higher-level language C
• Ritchie was found dead on October 12, 2011, at the age of 70 at his home in
Berkeley Heights, New Jersey, where he lived alone. First news of his death came from
his former colleague, Rob Pike. The cause and exact time of death have not been
disclosed.
re: https://en.wikipedia.org/wiki/Multics
re: https://en.wikipedia.org/wiki/History_of_Unix
re: https://en.wikipedia.org/wiki/Ken_Thompson
re: https://en.wikipedia.org/wiki/Dennis_Ritchie#C_and_Unix

4. BSD
• BSD: Berkeley Software Distribution
• A branch of Unix, Berkeley Unix
• Solaris
• FreeBSD, OpenBSD, NetBSD
• Darwin, macOS, iOS, watchOS, tvOS
• Berkeley sockets
• Bill Joy & Chuck Haley
• vi text editor
• Sun Microsystems, Inc
• Java programming language
Linux: I’m coming …
re: https://en.wikipedia.org/wiki/Berkeley_Software_Distribution
re: https://en.wikipedia.org/wiki/History_of_the_Berkeley_Software_Distribution
re: https://en.wikipedia.org/wiki/Berkeley_sockets

5. Unix philosophy
• The Unix philosophy, originated by Ken Thompson, is a set
of cultural norms and philosophical approaches to
minimalist, modular software development.
• The Unix philosophy favors composability as opposed to
monolithic design.
• Peter H. Salus in A Quarter-Century of Unix (1994):
• Write programs that do one thing and do it well.
• Write programs to work together.
• Write programs to handle text streams, because that is a
universal interface.
re: https://en.wikipedia.org/wiki/Unix_philosophy

6. GNU/Linux/Linux distribution
• Debian apt deb
• Ubuntu
• Fedora, Red Hat. yum rpm
• Red Hat Enterprise Linux (RHEL)
• CentOS
• Android
re: https://en.wikipedia.org/wiki/Linux
re: https://en.wikipedia.org/wiki/Linux_distribution

7. Debian on VM
• Oracle VirtualBox/VMware Player
• APT: Advanced Package Tool
• Shell/SSH/Putty/Xshell
• File/File System
• Process
• User/Group
• File System Permissions
• Signal
• Standard IO/Pipeline
• Vim: God of the text editors / Emacs: a text editor of the Gods

8. VirtualBox/VMware: Just do IT
• https://www.virtualbox.org/
• Download VirtualBox:
https://www.virtualbox.org/wiki/Downloads
• Download VMware Workstation Player:
https://my.vmware.com/en/web/vmware/free#desktop_end_user_co
mputing/vmware_workstation_player/12_0
• Getting Debian:
https://www.debian.org/distrib/
https://www.debian.org/mirror/list
• Download CentOS:
https://www.centos.org/download/
https://www.centos.org/download/mirrors/

9. APT: Advanced Package Tool
# apt-get update # yum makecache
Hit:1 https://deb.nodesource.com/node_8.x stretch InRelease
Hit:2 https://download.docker.com/linux/debian stretch InRelease
...
Reading package lists... Done
# apt-cache search nginx # yum search
nginx - small, powerful, scalable web/proxy server
# apt-cache madison nginx # yum --showduplicates search nginx
nginx | 1.13.3-1~bpo9+1 | http://mirrors.163.com/debian stretch-backports/main amd64 Packages
nginx | 1.10.3-1+deb9u1 | http://mirrors.163.com/debian stretch/main amd64 Packages
# apt-get install nginx # yum install nginx
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
...
re: https://en.wikipedia.org/wiki/APT_(Debian)

10. Shell/SSH/Putty/Xshell
$ touch hello.sh
$ cat <<EOF
> #!/bin/bash
>
> echo "Hello GNU/Linux!"
> EOF
#!/bin/bash
echo "Hello GNU/Linux!"
$ /bin/bash hello.sh
Hello GNU/Linux!
$ chmod +x hello.sh
$ ./hello.sh
Hello GNU/Linux!
$
re: https://en.wikipedia.org/wiki/Unix_shell
re: https://en.wikipedia.org/wiki/Bash_(Unix_shell)
re;: https://en.wikipedia.org/wiki/Secure_Shell

11. Bash - GNU Bourne-Again SHell
• Bash is an sh-compatible command language interpreter that executes commands
read from the standard input or from a file.
• Bash also incorporates useful features from the Korn and C shells (ksh and csh).
• A login shell is one whose first character of argument zero is a -, or one started with
the --login option.
• An interactive shell is one started without non-option arguments (unless -s is
specified) and without the -c option whose standard input and error are both
connected to terminals (as determined by isatty(3)), or one started with the -i option.
PS1 is set and $- includes i if bash is interactive, allowing a shell script or a startup
file to test this state.
• When you log in on a text console, or through SSH, or with su -, you get an
interactive login shell.
• When you start a shell in a terminal in an existing session (screen, X terminal, Emacs
terminal buffer, a shell inside another, etc.), you get an interactive, non-login shell.

12. Continued: Bash Startup Files
login non-login
interactive /etc/profile
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
non-interactive /etc/profile
~/.bash_profile
~/.bash_login
~/.profile
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
Typically, the ~/.bash_profile contains the line: if [ -f ~/.bashrc ]; then . ~/.bashrc; fi
re: https://www.gnu.org/software/bash/manual/html_node/Bash-Startup-Files.html
re: https://unix.stackexchange.com/questions/38175/difference-between-login-shell-and-non-login-shell
re: https://askubuntu.com/questions/879364/differentiate-interactive-login-and-non-interactive-non-login-shell

13. Continued: Subshell
• A subshell is a child process (fork`-
exec) launched by a shell (or shell
script).
• The source command can be used to
load any functions file into the current
shell script or a command prompt.
re: https://en.wikipedia.org/wiki/Fork%E2%80%93exec
re:
https://en.wikibooks.org/wiki/A_Quick_Introduction_to_Unix/She
lls_and_subshells
re: http://www.tldp.org/LDP/abs/html/subshells.html
$ cat hello.sh
#!/bin/bash
greeting="Hello GNU/Linux!"
$ ./hello.sh
$ echo $greeting
$ . ./hello.sh # source ./hello.sh
$ echo $greeting
Hello GNU/Linux!

14. Continued: ENVIRONMENT
• When a program is invoked it is given an array of strings called the
environment. This is a list of name-value pairs, of the form
name=value.
• The shell provides several ways to manipulate the environment. On
invocation, the shell scans its own environment and creates a
parameter for each name found, automatically marking it for export
to child processes. Executed commands inherit the
environment. The export and declare -x commands allow
parameters and functions to be added to and deleted from the
environment. If the value of a parameter in the environment is
modified, the new value becomes part of the environment,
replacing the old. The environment inherited by any executed
command consists of the shell's initial environment, whose values
may be modified in the shell, less any pairs removed by the unset
command, plus any additions via the export and declare -x
commands.
$ greeting="Hello GNU/Linux!"
$ echo $greeting
Hello GNU/Linux!
$ vi hello.sh
$ cat hello.sh
#!/bin/bash
echo $greeting
$ ./hello.sh
$ export greeting
$ ./hello.sh
Hello GNU/Linux!
$

15. File/File System
• "On a UNIX system, everything is a
file; if something is not a file, it is
a process.“
• Sorts of files
• - Regular file
• d Directory
• l Link
• c Character device
• s Socket
• p Named pipe
• b Block device
re: http://www.tldp.org/LDP/intro-
linux/html/sect_03_01.html
re:
https://en.wikipedia.org/wiki/File_system
# mkdir mydir
# touch myfile
# ln -sf myfile mylink
# ls -l
total 4
drwxr-xr-x 2 root root 4096 Sep 10 17:10 mydir
-rw-r--r-- 1 root root 0 Sep 10 17:10 myfile
lrwxrwxrwx 1 root root 6 Sep 10 17:10 mylink -> myfile
# ls -l /var/run/*.sock
srw-rw---- 1 root docker 0 Sep 10 11:01 /var/run/docker.sock
# ls -l /dev/sda1
brw-rw---- 1 root disk 8, 1 Sep 10 11:01 /dev/sda1
# ls -l /dev/tty1
crw--w---- 1 root tty 4, 1 Sep 10 11:01 /dev/tty1

16. Continued: File/File System
/tmp$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 986M 0 986M 0% /dev
tmpfs 200M 6.1M 194M 4% /run
/dev/sda1 19G 9.9G 7.9G 56% /
tmpfs 998M 0 998M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 998M 0 998M 0% /sys/fs/cgroup
tmpfs 200M 0 200M 0% /run/user/1000
/tmp$ df . -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 19G 9.9G 7.9G 56% /
/tmp$ touch foobar
/tmp$ ls -li foobar
262826 -rw-r--r-- 1 x x 0 Sep 11 21:01 foobar

17. Continued: File/File System
/tmp# mkdir mydir # make a directory
/tmp# cd mydir/ # change to mydir/
/tmp/mydir# pwd # print the work directory
/tmp/mydir
/tmp/mydir# touch myfile # make a file
/tmp/mydir# ls # list the currenty directory contents
myfile
/tmp/mydir# mv myfile myfile2 # rename myfile to myfile2
/tmp/mydir# rm myfile2 # remove myfile2
/tmp/mydir# cd .. # change to parent dir
/tmp# rm -r mydir/ # remove mydir
/tmp# ls
/tmp#
/tmp# cat <<EOF > foo
> Hello GNU/Linux!
> EOF
/tmp# cat foo
Hello GNU/Linux!
/tmp# cp foo bar # copy foo to bar
/tmp# ls
bar foo
/tmp# cat bar
Hello GNU/Linux!
/tmp# mkdir mydir
/tmp# mv foo bar mydir/ # move foo bar to mydir/
/tmp# ls
mydir
/tmp# cp -a mydir/ mydir2 # copy mydir/ to mydir2
/tmp# ls
mydir mydir2

18. Continued: File/File System
/tmp# cat <<EOF > hello.sh
> #!/bin/bash
> echo "Hello GNU/Linux!"
> EOF
/tmp# ls -l
total 4
-rw-r--r-- 1 root root 36 Sep 10 17:34 hello.sh
/tmp# chmod +x hello.sh
/tmp# ls -l
total 4
-rwxr-xr-x 1 root root 36 Sep 10 17:34 hello.sh
/tmp# ./hello.sh
Hello GNU/Linux!
/tmp# stat -c "%a" hello.sh
755
/tmp# chmod 777 hello.sh
/tmp# ls -l
total 4
-rwxrwxrwx 1 root root 36 Sep 10 17:34 hello.sh
/tmp# tail -n 1 hello.sh
echo "Hello GNU/Linux!"
/tmp# head -n 1 hello.sh
#!/bin/bash
/tmp# cat hello.sh
#!/bin/bash
echo "Hello GNU/Linux!"

19. Continued: File/File System
$ tree -L 2 webdissector/website/
webdissector/website/
├── NuGet.config
├── src
│ ├── Gridsum.WebDissector.Authentication
│ ├── Gridsum.WebDissector.Glimpse
│ ├── Gridsum.WebDissector.Metadata.Models
│ ├── Gridsum.WebDissector.Metadata.Resources
│ ├── Gridsum.WebDissector.Realtime
│ ├── Gridsum.WebDissector.SqlBuilder
│ ├── WebDissectorV3
│ └── WebDissectorV3.Models
├── test
│ ├── Gridsum.WebDissector.Authentication.Test
│ ├── Gridsum.WebDissector.SqlBuilder.Tests
│ └── WebDissectorV3.Testing
├── tools
│ └── Gridsum.WebDissector.ConfigurationMigrationApp
└── WebDissectorV3.sln
15 directories, 2 files

20. Continued: File/File System
/bin Common programs, shared by the system, the system administrator and the users.
/boot The startup files and the kernel, vmlinuz.
/dev Contains references to all the CPU peripheral hardware, which are represented as files with special properties.
/etc Most important system configuration files are in /etc, this directory contains data similar to those in the Control Panel in Windows
/home Home directories of the common users.
/lib Library files, includes files for all kinds of programs needed by the system and the users.
/mnt Standard mount point for external file systems, e.g. a CD-ROM or a digital camera.
/opt Typically contains extra and third party software.
/proc A virtual file system containing information about system resources.
/root The administrative user's home directory.
/sbin Programs for use by the system and the system administrator.
/tmp Temporary space for use by the system, cleaned upon reboot, so don't use this for saving any work!
/usr Programs, libraries, documentation etc. for all user-related programs.
/var Storage for all variable files and temporary files created by.

21. Process
$ ps -f -C nginx
UID PID PPID C STIME TTY TIME CMD
root 6630 1 0 21:43 ? 00:00:00 nginx: master process nginx
www-data 6631 6630 0 21:43 ? 00:00:00 nginx: worker process
www-data 6632 6630 0 21:43 ? 00:00:00 nginx: worker process
$ ps aux|grep nginx
root 6630 0.0 0.0 159484 1640 ? Ss 21:43 0:00 nginx: master process nginx
www-data 6631 0.0 0.1 159840 3412 ? S 21:43 0:00 nginx: worker process
www-data 6632 0.0 0.1 159840 3412 ? S 21:43 0:00 nginx: worker process
$ ps -f -u www-data
UID PID PPID C STIME TTY TIME CMD
www-data 6631 6630 0 21:43 ? 00:00:00 nginx: worker process
www-data 6632 6630 0 21:43 ? 00:00:00 nginx: worker process

22. Continued: Process
$ pstree -p
systemd(1)─┬─acpid(422)
├─agetty(435)
├─cron(354)
├─dbus-daemon(360)
├─dhclient(477)
├─irqbalance(358)
├─ntpd(446)───{ntpd}(455)
├─rsyslogd(359)─┬─{in:imklog}(403)
│ ├─{in:imuxsock}(402)
│ └─{rs:main Q:Reg}(404)
├─sshd(353)───sshd(1360)───sshd(1369)───bash(1370)───pstree(3168)
├─systemd(1362)───(sd-pam)(1363)
├─systemd-journal(197)
├─systemd-logind(417)
└─systemd-udevd(211)

23. Continued: Process
# pstree -p
init(1)─┬─acpid(2155)
├─auditd(2052)─┬─audispd(2054)───{audispd}(2055)
│ └─{auditd}(2053)
├─dhclient(2001)
├─events/0(4)
├─klogd(2087)
├─ksoftirqd/0(3)
├─kthread(6)─┬─aio/0(245)
│ ├─ata/0(498)
├─smartd(2338)
├─sshd(2244)───sshd(2395)───sshd(2402)───bash(2403)───su(2435)───bash(2436)───pstree(2519)
├─syslogd(2084)
└─udevd(575)

24. User/Group
$ touch foo
$ sudo touch bar
$ ls -l
total 0
-rw-r--r-- 1 root root 0 Sep 11 21:57 bar
-rw-r--r-- 1 x x 0 Sep 11 21:57 foo
$ chown x bar
chown: changing ownership of 'bar': Operation not permitted
$ sudo chown x bar
$ ls -l
total 0
-rw-r--r-- 1 x root 0 Sep 11 21:57 bar
-rw-r--r-- 1 x x 0 Sep 11 21:57 foo
$ sudo chgrp x bar
$ ls -l
total 0
-rw-r--r-- 1 x x 0 Sep 11 21:57 bar
-rw-r--r-- 1 x x 0 Sep 11 21:57 foo$
$ ps -f -C nginx,ps
UID PID PPID C STIME TTY TIME CMD
root 6630 1 0 21:43 ? 00:00:00 nginx: master process nginx
www-data 6631 6630 0 21:43 ? 00:00:00 nginx: worker process
www-data 6632 6630 0 21:43 ? 00:00:00 nginx: worker process
x 6872 3315 0 22:02 pts/1 00:00:00 ps -f -C nginx,ps
$ sudo touch foobar
[sudo] password for x:
$ echo 'Hello GNU/Linux!' > foobar
-bash: foobar: Permission denied
$ ls -l foobar
-rw-r--r-- 1 root root 0 Sep 12 13:56 foobar
$ su
Password:
# echo 'Hello GNU/Linux!' > foobar
# exit
exit
$ id
uid=1000(x) gid=1000(x)
groups=1000(x),24(cdrom),25(floppy),27(sudo),29(audio),30(dip),44(video),46(plugdev),108(netdev),999(
docker)
$ sudo grep '%sudo' /etc/sudoers
%sudo ALL=(ALL:ALL) ALL$

25. Continued: User/Group
~# cd ~xianyu
-su: cd: ~xianyu: No such file or directory
~# useradd -s /bin/bash -u 2000 -c "Hello GNU/Linux!" -m xianyu
~# cd ~xianyu/
/home/xianyu# grep 'xianyu' /etc/passwd
xianyu:x:2000:2000:Hello GNU/Linux!:/home/xianyu:/bin/bash
/home/xianyu# id xianyu
uid=2000(xianyu) gid=2000(xianyu) groups=2000(xianyu)
/home/xianyu# su - xianyu
~$ pwd
/home/xianyu
~$ exit
logout
/home/xianyu# cd
~# userdel -r xianyu
userdel: xianyu mail spool (/var/mail/xianyu) not found
~# cd ~xianyu
-su: cd: ~xianyu: No such file or directory
~#

26. File System Permissions
Symbolic Notation Numeric Notation English
---------- 0000 no permissions
-rwx------ 0700 read, write, & execute only for owner
-rwxrwx--- 0770 read, write, & execute for owner and group
-rwxrwxrwx 0777 read, write, & execute for owner, group and others SECURITY RISK
---x--x--x 0111 execute
--w--w--w- 0222 write
--wx-wx-wx 0333 write & execute
-r--r--r-- 0444 read
-r-xr-xr-x 0555 read & execute
-rw-rw-rw- 0666 read & write
-rwxr----- 0740 owner can read, write, & execute; group can only read; others have no permissions
re: https://en.wikipedia.org/wiki/File_system_permissions
re: https://en.wikipedia.org/wiki/Umask

27. Continued: File System Permissions
# umask
0022
# umask -S
u=rwx,g=rx,o=rx
# touch hello.sh
# stat -c "%a" hello.sh
644
# ls -l hello.sh
-rw-r--r-- 1 root root 0 Sep 12 15:03 hello.sh
# cat <<EOF > hello.sh
> #!/bin/bash
> echo "Hello GNU/Linux!"
> EOF
# ./hello.sh
-su: ./hello.sh: Permission denied
# su x
$ ./hello.sh
bash: ./hello.sh: Permission denied
$ sudo chmod o+x hello.sh
$ ./hello.sh
Hello GNU/Linux!
$ ls -l hello.sh
-rwxr--r-x 1 root root 36 Sep 12 15:04 hello.sh
$ sudo chmod g+x hello.sh
$ ls -l hello.sh
-rwxr-xr-x 1 root root 36 Sep 12 15:04 hello.sh
$ sudo chmod 777 hello.sh
$ ls -l hello.sh
-rwxrwxrwx 1 root root 36 Sep 12 15:04 hello.sh

28. Signal (IPC=Inter-process communication)
$ kill -l
1) SIGHUP 2) SIGINT(Ctrl-C) 3) SIGQUIT(Ctrl-) 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP(Ctrl-Z ) 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX

29. Standard IO/Pipeline
$ ls -l /dev/std*
lrwxrwxrwx 1 root root 15 Sep 12 09:28 /dev/stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root root 15 Sep 12 09:28 /dev/stdin -> /proc/self/fd/0
lrwxrwxrwx 1 root root 15 Sep 12 09:28 /dev/stdout -> /proc/self/fd/1
$ ls -l /proc/self/fd/{0,1,2}
lrwx------ 1 x x 64 Sep 12 20:15 /proc/self/fd/0 -> /dev/pts/0
lrwx------ 1 x x 64 Sep 12 20:15 /proc/self/fd/1 -> /dev/pts/0
lrwx------ 1 x x 64 Sep 12 20:15 /proc/self/fd/2 -> /dev/pts/0
re: https://en.wikipedia.org/wiki/Standard_streams
re: https://en.wikipedia.org/wiki/Redirection_(computing)
$ cat hello.sh
#!/bin/bash
echo "Hello GNU/Linux!"
foo bar
$ ./hello.sh
Hello GNU/Linux!
./hello.sh: line 3: foo: command not found
$ ./hello.sh 2> err 1> out
$ cat err
./hello.sh: line 3: foo: command not found
$ cat out
Hello GNU/Linux!
$ ./hello.sh > allblue 2>&1
$ cat allblue
Hello GNU/Linux!
./hello.sh: line 3: foo: command not found
$ cat < out | xargs echo
Hello GNU/Linux!

30. Continued: Standard IO/Pipeline
• In Unix-like computer operating systems, a pipeline is a
sequence of processes chained together by their standard
streams, so that the output of each process (stdout) feeds
directly as input (stdin) to the next one.
• The concept of pipelines was championed by Douglas
McIlroy at Unix's ancestral home of Bell Labs, during the
development of Unix, shaping its toolbox philosophy.
• Each process takes input from the previous process and
produces output for the next process via standard streams.
Each "|" tells the shell to connect the standard output of
the command on the left to the standard input of the
command on the right by an inter-process communication
mechanism called an (anonymous) pipe, implemented in
the operating system. Pipes are unidirectional; data flows
through the pipeline from left to right.
re: https://en.wikipedia.org/wiki/Pipeline_%28Unix%29

31. Continued: Standard IO/Pipeline
$ man 1 man | less
$ git rebase –-help | more

32. Vim: God of the text editors
• Two modes: command mode and insert mode
• Commands that switch the editor to insert mode
a will append: it moves the cursor one position to the
right before switching to insert mode
i will insert
o will insert a blank line under the current cursor
position and move the cursor to that line.
• Moving through the text
h to move the cursor to the left
l to move it to the right
k to move up
j to move down
re: https://vim.org
Basic operations
n dd will delete n lines starting from the current cursor
position.
n dw will delete n words at the right side of the cursor.
x will delete the character on which the cursor is positioned
:n moves to line n of the file.
:w will save (write) the file
:q will exit the editor.
:q! forces the exit when you want to quit a file containing
unsaved changes.
:wq will save and exit
:w newfile will save the text to newfile.
:wq! overrides read-only permission (if you have the permission
to override permissions, for instance when you are using the root
account.
/astring will search the string in the file and position the
cursor on the first match below its position.
:1, $s/word/anotherword/g will replace word with anotherword
throughout the file.
yy will copy a block of text.

33. Vim: God of the text editors
Demo

34. Thanks
Q&A