02 Linux - Fundamentals

Shell Commands
Contents
What is a Shell?
Shell commands
Why to use CLI over GUI?
● Less resources ( graphics components add to more required memory )
● High precision
● Repeatative tasks friendly
● Powerful
But always remember.......
Image source - https://knowyourmeme.com/memes/with-great-power-comes-great-responsibility

What is a Shell ?
● Shell is a command language interpreter that
executes commands read from the standard
input device (keyboard) or any file.
● Shell is not a part of system kernel but uses the
kernel to execute programs.
● cat /etc/shells command will give the various
shells in our system.
● Sh – simple shell
● BASH – Bourne Again Shell
● KSH – Korne Shell
● CSH – C Shell
● SSH – Secure Shell

Want to check which type of Shell you are using?
echo $SHELL
How to check what a particular command do?
● man <command>
● e.g. man ls
How to check the list of files in a folder?
● ls -a <folder> (all)Lists all the files (including .*files)
● ls -l <folder> (long) Long listing (type, date, size,owner, permissions)
● ls -t <folder> (time) Lists the most recent files first
● ls -S <folder> (size) Lists the biggest files first
● ls -r <folder> (reverse) Reverses the sort order
● ls -ltr <folder> (options can be combined) Long listing, most recent files at the end
File name pattern substitutions
ls *txt
The shell first replaces *txt by all the file and directory names ending by txt (including .txt), except
those starting with ., and then executes the ls command line. This will work when you are
inside the directory.
ls -d .*
Lists all the files and directories starting with “.” and d tells ls not to display the contents of
directories.
Thats great that it worked but what was . And .. ?
cat ?.log
Displays all the files which names start by 1 character and end by .log
Working with directories
command function
pwd print working directory
mkdir dirName make directory
mkdir -p dirName create parent directory
rmdir dirName remove directory
rm -r dirName or rm -ri dirName or rm -rf dirName remove dir recursively (add f for force), -i with permission
cd /dirName/dirPath go to a specific dir
cd takes you to home directory
cd ~ home directory
cd .. previous directory
cd - previous dir with path
Practice: working with directories
● Display your current directory. ● Stay where you are, and list the contents of
● Change to the /etc directory. ~.
● Now change to your home directory using ● List all the files (including hidden files) in your
only three key presses. home directory.
● Change to the /boot/grub directory using only ● List the files in /boot in a human readable
eleven key presses. format.
● Go to the parent directory of the current ● Create a directory testdir in your home
directory. directory.
● Go to the root directory. ● Change to the /etc directory, stay here and
● List the contents of the root directory. create a directory newdir in your home
● List a long listing of the root directory. directory.
● Stay where you are, and list the contents of ● Create in one command the directories
/etc. ~/dir1/dir2/dir3 (dir3 is a subdirectory from
dir2, and dir2 is a subdirectory from dir1 ).
● Stay where you are, and list the contents of
/bin and /sbin. ● Remove the directory testdir.
Working with files
“Everything in Linux is a file, Everything in Linux that is not a file is a process”
Let’s learn how to recognise, create, remove, copy and move files using commands:
command function
touch filename1 fileName2 fileName3 …. easy way to create a file
cp file1 file2 or cp fileName filePath copy content of a file to other file
mv fileName1 fileName2 or mv fileName1 filePath/dirPath move file content or file to other dir
cp -r dirName1 dirName2 recursive copy
cp file1 file2 file3 file4 file5 /dirName cp multiple files to directory
head display first 10 lines
tail display last 10 lines
cat display content
cat > fileName create file with concatenated content (ctrl+d for EOL)
File, Users, Groups and Permissions
Users, Groups and Permissions
● Use ls -l to check file access rights
● 3 types of access rights
● Read access (r)
● Write access (w)
● Execute rights (x)
● 3 types of access levels
● User (u): for the owner of the file
● Group (g): each file also has a “group” attribute, corresponding to a given list of users
● Others (o): for all other users
Changing permissions
chmod <permissions> <files>
sudo chmod --- fileName
1. Numerical values
Read = 4 , write = 2 , execute = 1
e.g.
-r--r--r-- 1 sagar sagar 7 Jul 21 21:14 te2.txt
-rw-rw-rw- 1 sagar sagar 7 Jul 21 21:14 te2.txt

Changing permissions
● 2. Symbolic way
− chmod go+r: add read permissions to group and others.
− chmod u-w: remove write permissions from user.
− chmod a-x: (a: all) remove execute permission from all.
− chmod R a+rX linux/: Makes linux and everything in it available to everyone!
−R: apply changes recursively
− X: x, but only for directories and files already executable
File ownership
● Particularly useful in (embedded) system development when you create files for another
system.
● We should have multiple users to change ownership, add a user first:
○ sudo adduser username
■ sudo adduser sco
○ to delete a user:
■ sudo deluser username
Now create a file/dir and change owner

● chown -R sco /home/linux/src (R: recursive) Makes user sco the new owner of all the files
in /home/linux/src.
● chgrp -R empire /home/askywalker: Makes empire the new group of everything in
● /home/askywalker.
The root account
● In case you really want to use root.
● If you have the root password:
● sudo -s(switch user)
● sudo command gives you access to some root privileges with your own user password.
● for example sudo chmod 777 fileName.sh
Standard I/O, redirections, pipes
● More about command output
● All the commands outputting text on your terminal do it by writing to their standard output.
● echo content - outputs the strings it is being passed as arguments
● > redirectional operator a standard output can be written (redirected) to a file
● >> Standard output can be appended to an existing file
● echo “Welcome to NSTI, Bangalore” > sample.txt
● echo “how’s your day going?” >> sample.txt
command function
grep pattern fileName searches a file or files for lines that have a certain pattern
| pipe Pipes '|' send the output of one command as input of another command.
sort 'sort' command sorts out the content of a file alphabetically

● e.g.
● grep "123" te4.txt | cat > te7.txt
● Process and jobs
● “Everything in Unix is a file , Everything in Unix that is not a file is a process”
● Instances of a running programs
● Several instances of the same program can run at the same time
● Data associated to processes:
● Open files, allocated memory, stack, process id, parent, priority, state...
● PID: Process id
● VSZ: Virtual process size (code + data + stack)
● RSS: Process resident size: number of KB currently in RAM
● TTY: Terminal
● STAT: Status: R (Runnable), S (Sleep), W (paging), Z (Zombie)...
ps ux Lists all the processes belonging to the current user
top Displays most important processes, sorted by cpu percentage
kill <pids> Sends an abort signal to the given processes. Lets processes save data and exit by themselves
kill 9 <pids> Sends an immediate termination signal
pstree display a tree of processes

Environment variables
Shells let the user define variables. They can be reused in shell commands.
Convention: lower case names
variables that are also visible within scripts or executables called from the shell.
Convention: upper case names.
env Lists all defined environment variables and their value.
SHELL Current shell name
TERM Current terminal type
USER Current user name
HOSTNAME Name of the local machine
PATH Command search path

● ~/.bashrc file
● Shell script read each time a bash shell is started
● You can use this file to define
● Your default environment variables (PATH, EDITOR...).
● Your aliases.
● A greeting message.
● Miscellaneous
du -h <file> returns size on disk of the given file
df -h Returns disk usage and free space for the filesystem containing the given directory.
tar -cvf <archive> <files or c: create

v: verbose. Useful to follow archiving progress.
directories> f: file. Archive created in file (tape used otherwise).
tar -cvf sample.tar sample

tar -xvf <archive> x - extract
gzip fileName create gz file (gnu zip)

● Getting information about users
● text editors
● vi
● vim
● nano
● gedit

02 Linux - Fundamentals

Uploaded by

Copyright:

Available Formats

02 Linux - Fundamentals

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

02 Linux - Fundamentals

Uploaded by

Copyright:

Available Formats

Shell Commands

Image source - https://knowyourmeme.com/memes/with-great-power-comes-great-responsibility

● SSH – Secure Shell

touch filename1 fileName2 fileName3 …. easy way to create a file

cp file1 file2 or cp fileName filePath copy content of a file to other file

cp -r dirName1 dirName2 recursive copy

cp file1 file2 file3 file4 file5 /dirName cp multiple files to directory

head display first 10 lines

tail display last 10 lines

cat display content

sudo chmod --- fileName

Read = 4 , write = 2 , execute = 1

-r--r--r-- 1 sagar sagar 7 Jul 21 21:14 te2.txt

-rw-rw-rw- 1 sagar sagar 7 Jul 21 21:14 te2.txt

Now create a file/dir and change owner

sort 'sort' command sorts out the content of a file alphabetically

top Displays most important processes, sorted by cpu percentage

kill 9 <pids> Sends an immediate termination signal

pstree display a tree of processes

env Lists all defined environment variables and their value.

SHELL Current shell name

TERM Current terminal type

USER Current user name

HOSTNAME Name of the local machine

PATH Command search path

du -h <file> returns size on disk of the given file

tar -cvf <archive> <files or c: create

tar -cvf sample.tar sample

gzip fileName create gz file (gnu zip)

You might also like