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About Bash projects

Unless stated, all your projects will be auto-corrected with Ubuntu 20.04 LTS.

Concepts

For this project, we expect you to look at this concept:

Resources

Read or watch:

man or help:

  • printenv
  • set
  • unset
  • export
  • alias
  • unalias
  • .
  • source
  • printf

Learning Objectives

At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

General

  • What happens when you type $ ls -l *.txt

Shell Initialization Files

  • What are the /etc/profile file and the /etc/profile.d directory
  • What is the ~/.bashrc file

Variables

  • What is the difference between a local and a global variable
  • What is a reserved variable
  • How to create, update and delete shell variables
  • What are the roles of the following reserved variables: HOME, PATH, PS1
  • What are special parameters
  • What is the special parameter $??

Expansions

  • What is expansion and how to use them
  • What is the difference between single and double quotes and how to use them properly
  • How to do command substitution with $() and backticks

Shell Arithmetic

  • How to perform arithmetic operations with the shell

The alias Command

  • How to create an alias
  • How to list aliases
  • How to temporarily disable an alias

Other help pages

How to execute commands from a file in the current shell

Requirements

General

  • Allowed editors: vi, vim, emacs
  • All your scripts will be tested on Ubuntu 20.04 LTS
  • All your scripts should be exactly two lines long ($ wc -l file should print 2)
  • All your files should end with a new line (why?)
  • The first line of all your files should be exactly #!/bin/bash
  • A README.md file, at the root of the folder of the project, describing what each script is doing
  • You are not allowed to use &&, || or ;
  • You are not allowed to use bc, sed or awk
  • All your files must be executable

More Info

Read your /etc/profile, /etc/inputrc and ~/.bashrc files.

Look at some files in the /etc/profile.d directory.

Note: You do not have to learn about awk, tar, bzip2, date, scp, ulimit, umask, or shell scripting, yet.

Quiz questions

Question #0

Which command should I use to display a variable?

  • echo $MYVAR

  • ls $MYVAR

  • cd $MYVAR

  • export $MYVAR

Question #1

Which command should I use to define a new command push for pushing in Github?

Example:

$ push
Everything up-to-date
$

  • export push=git push

  • alias push="git push"

  • export push="git push"

  • alias push=git push

Question #2

What is the variable name who contains the previous working directory path?

  • PREVDIR

  • OLDPWD

  • PREVPWD

  • OLDDIR

Question #3

Which command should I use to display the exit code of the previous command?

  • echo $CODE

  • echo ?

  • echo $EXITCODE

  • echo $?

Tasks

0.

Create a script that creates an alias.

  • Name: ls
  • Value: rm *
julien@ubuntu:/tmp/0x03$ ls
0-alias  file1  file2
julien@ubuntu:/tmp/0x03$ source ./0-alias
julien@ubuntu:/tmp/0x03$ ls
julien@ubuntu:/tmp/0x03$ \ls
julien@ubuntu:/tmp/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 0-alias

1. Hello you

Create a script that prints hello user, where user is the current Linux user.

julien@ubuntu:/tmp/0x03$ id
uid=1000(julien) gid=1000(julien) groups=1000(julien),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lpadmin),128(sambashare)
julien@ubuntu:/tmp/0x03$ ./1-hello_you
hello julien
julien@ubuntu:/tmp/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 1-hello_you

2. The path to success is to take massive, determined action

Add /action to the PATH. /action should be the last directory the shell looks into when looking for a program.

julien@ubuntu:/tmp/0x03$ echo $PATH
/home/julien/bin:/home/julien/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
julien@ubuntu:/tmp/0x03$ source ./2-path
julien@ubuntu:/tmp/0x03$ echo $PATH
/home/julien/bin:/home/julien/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/action
julien@ubuntu:/tmp/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 2-path

3. If the path be beautiful, let us not ask where it leads

Create a script that counts the number of directories in the PATH.

julien@ubuntu:/tmp/0x03$ echo $PATH
/home/julien/bin:/home/julien/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
julien@ubuntu:/tmp/0x03$ . ./3-paths
11
julien@ubuntu:/tmp/0x03$ PATH=/home/julien/bin:/home/julien/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:::::/hello
julien@ubuntu:/tmp/0x03$ . ./3-paths
12
julien@ubuntu:/tmp/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 3-paths

4. Global variables

Create a script that lists environment variables.

julien@ubuntu:/tmp/0x03$ source ./4-global_variables
CC=gcc
CDPATH=.:~:/usr/local:/usr:/
CFLAGS=-O2 -fomit-frame-pointer
COLORTERM=gnome-terminal
CXXFLAGS=-O2 -fomit-frame-pointer
DISPLAY=:0
DOMAIN=hq.garrels.be
e=
TOR=vi
FCEDIT=vi
FIGNORE=.o:~
G_BROKEN_FILENAMES=1
GDK_USE_XFT=1
GDMSESSION=Default
GNOME_DESKTOP_SESSION_ID=Default
GTK_RC_FILES=/etc/gtk/gtkrc:/nethome/franky/.gtkrc-1.2-gnome2
GWMCOLOR=darkgreen
GWMTERM=xterm
HISTFILESIZE=5000
history_control=ignoredups
HISTSIZE=2000
HOME=/nethome/franky
HOSTNAME=octarine.hq.garrels.be
INPUTRC=/etc/inputrc
IRCNAME=franky
JAVA_HOME=/usr/java/j2sdk1.4.0
LANG=en_US
LDFLAGS=-s
LD_LIBRARY_PATH=/usr/lib/mozilla:/usr/lib/mozilla/plugins
LESSCHARSET=latin1
LESS=-edfMQ
LESSOPEN=|/usr/bin/lesspipe.sh %s
LEX=flex
LOCAL_MACHINE=octarine
LOGNAME=franky
[...]
julien@ubuntu:/tmp/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 4-global_variables

5. Local variables

Create a script that lists all local variables and environment variables, and functions.

julien@ubuntu:/tmp/0x03$ . ./5-local_variables
BASH=/bin/bash
BASHOPTS=checkwinsize:cmdhist:complete_fullquote:expand_aliases:extglob:extquote:force_fignore:histappend:interactive_comments:progcomp:promptvars:sourcepath
BASH_ALIASES=()
BASH_ARGC=()
BASH_ARGV=()
BASH_CMDS=()
BASH_COMPLETION_COMPAT_DIR=/etc/bash_completion.d
BASH_LINENO=()
BASH_REMATCH=()
BASH_SOURCE=()
BASH_VERSINFO=([0]="4" [1]="3" [2]="46" [3]="1" [4]="release" [5]="x86_64-pc-linux-gnu")
BASH_VERSION='4.3.46(1)-release'
CLUTTER_IM_MODULE=xim
COLUMNS=133
COMPIZ_CONFIG_PROFILE=ubuntu
COMP_WORDBREAKS=$' \t\n"\'><=;|&(:'
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-Fg27Lr20bq
DEFAULTS_PATH=/usr/share/gconf/ubuntu.default.path
DESKTOP_SESSION=ubuntu
[...]
julien@ubuntu:/tmp/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 5-local_variables

6. Local variable

Create a script that creates a new local variable.

  • Name: BEST
  • Value: School

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 6-create_local_variable

7. Global variable

Create a script that creates a new global variable.

  • Name: BEST
  • Value: School

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 7-create_global_variable

8. Every addition to true knowledge is an addition to human power

Write a script that prints the result of the addition of 128 with the value stored in the environment variable TRUEKNOWLEDGE, followed by a new line.

julien@production-503e7013:~$ export TRUEKNOWLEDGE=1209
julien@production-503e7013:~$ ./8-true_knowledge | cat -e
1337$
julien@production-503e7013:~$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 8-true_knowledge

9. Divide and rule

Write a script that prints the result of POWER divided by DIVIDE, followed by a new line.

  • POWER and DIVIDE are environment variables
julien@production-503e7013:~$ export POWER=42784
julien@production-503e7013:~$ export DIVIDE=32
julien@production-503e7013:~$ ./9-divide_and_rule | cat -e
1337$
julien@production-503e7013:~$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 9-divide_and_rule

10. Love is anterior to life, posterior to death, initial of creation, and the exponent of breath

Write a script that displays the result of BREATH to the power LOVE

  • BREATH and LOVE are environment variables
  • The script should display the result, followed by a new line
julien@production-503e7013:~/$ export BREATH=4
julien@production-503e7013:~/$ export LOVE=3
julien@production-503e7013:~/$ ./10-love_exponent_breath
64
julien@production-503e7013:~/$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 10-love_exponent_breath

11. There are 10 types of people in the world -- Those who understand binary, and those who don't

Write a script that converts a number from base 2 to base 10.

  • The number in base 2 is stored in the environment variable BINARY
  • The script should display the number in base 10, followed by a new line
julien@production-503e7013:~/$ export BINARY=10100111001
julien@production-503e7013:~/$ ./11-binary_to_decimal
1337
julien@production-503e7013:~/$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 11-binary_to_decimal

12. Combination

Create a script that prints all possible combinations of two letters, except oo.

  • Letters are lower cases, from a to z
  • One combination per line
  • The output should be alpha ordered, starting with aa
  • Do not print oo
  • Your script file should contain maximum 64 characters
julien@ubuntu:/tmp/0x03$ echo $((26 ** 2 -1))
675
julien@ubuntu:/tmp/0x03$ ./12-combinations | wc -l
675
julien@ubuntu:/tmp/0x03$
julien@ubuntu:/tmp/0x03$ ./12-combinations | tail -303 | head -10
oi
oj
ok
ol
om
on
op
oq
or
os
julien@ubuntu:/tmp/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 12-combinations

13. Floats

Write a script that prints a number with two decimal places, followed by a new line.

The number will be stored in the environment variable NUM.

ubuntu@ip-172-31-63-244:~/0x03$ export NUM=0
ubuntu@ip-172-31-63-244:~/0x03$ ./13-print_float
0.00
ubuntu@ip-172-31-63-244:~/0x03$ export NUM=98
ubuntu@ip-172-31-63-244:~/0x03$ ./13-print_float
98.00
ubuntu@ip-172-31-63-244:~/0x03$ export NUM=3.14159265359
ubuntu@ip-172-31-63-244:~/0x03$ ./13-print_float
3.14
ubuntu@ip-172-31-63-244:~/0x03$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 13-print_float

14. Decimal to Hexadecimal

Write a script that converts a number from base 10 to base 16.

  • The number in base 10 is stored in the environment variable DECIMAL
  • The script should display the number in base 16, followed by a new line
julien@production-503e7013:~/$ export DECIMAL=16
julien@production-503e7013:~/$ ./100-decimal_to_hexadecimal
10
julien@production-503e7013:~/$ export DECIMAL=1337
julien@production-503e7013:~/$ ./100-decimal_to_hexadecimal | cat -e
539$
julien@production-503e7013:~/$ export DECIMAL=15
julien@production-503e7013:~/$ ./100-decimal_to_hexadecimal | cat -e
f$
julien@production-503e7013:~/$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 100-decimal_to_hexadecimal

15. Everyone is a proponent of strong encryption

Write a script that encodes and decodes text using the rot13 encryption. Assume ASCII.

julien@production-503e7013:~/shell/fun_with_the_shell$ cat quote
"Everyone is a proponent of strong encryption."
- Dorothy E. Denning
julien@production-503e7013:~/shell/fun_with_the_shell$ ./101-rot13 < quote
"Rirelbar vf n cebcbarag bs fgebat rapelcgvba."
- Qbebgul R. Qraavat
julien@production-503e7013:~/shell/fun_with_the_shell$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 101-rot13

16. The eggs of the brood need to be an odd number

Write a script that prints every other line from the input, starting with the first line.

ubuntu@ip-172-31-63-244:/$ \ls -1
bin
boot
dev
etc
home
initrd.img
lib
lib32
lib64
libx32
lost+found
media
mnt
opt
proc
root
run
sbin
srv
sys
t
#t#
t~
tmp
usr
var
vmlinuz
whoareyou
ubuntu@ip-172-31-63-244:/$ \ls -1 | ./102-odd
bin
dev
home
lib
lib64
lost+found
mnt
proc
run
srv
t
t~
usr
vmlinuz
ubuntu@ip-172-31-63-244:/$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 102-odd

17. I'm an instant star. Just add water and stir.

Write a shell script that adds the two numbers stored in the environment variables WATER and STIR and prints the result.

  • WATER is in base water
  • STIR is in base stir.
  • The result should be in base bestchol
julien@production-503e7013:~$ export WATER="ewwatratewa"
julien@production-503e7013:~$ export STIR="ti.itirtrtr"
julien@production-503e7013:~$ ./103-water_and_stir
shtbeolhc
julien@production-503e7013:~$

Repo:

  • GitHub repository: alx-system_engineering-devops
  • Directory: 0x03-shell_variables_expansions
  • File: 103-water_and_stir