BASH Exercises

For easy reference to BASH scripting, check out devhints.io/bash

Hello World

create a script that prints:

Hello World

Answer

#!/bin/bash

echo "Hello World"

Utilities

create a script that prints:

Hello $username, it is $HH:MM" as terminal output 

Answer

#!/bin/bash

echo "Hello $(whoami), it is $(date +"%H:%M")"

Environment Variables

create a script that prints:

"My git editor: _"
"My default shell: _"

Answer

#!/bin/bash

echo "My git editor: $GIT_EDITOR"
echo "My default shell: $SHELL"

Shell Variables

create a script that prints:

Name of the script: _
First Argument: _
All arguments: _
Current PID: _

Answer

#!/bin/bash

echo "Name of the script: $0"
echo "First argument: $1"
echo "All arguments: $*"
echo "Current PID: $$"

Parameter Expansion

Substitution

create a script that replaces the word "world" with the word "planet" from the sentence "hello world". See parameter expansion

Answer

#!/bin/bash

string="hello world"

echo ${string/world/planet}

For Loops

create a script that counts from 1-10. Use a c-like for loop or a range or both!

Answer

#!/bin/bash

# c-like loop
for ((i = 1 ; i <= 10 ; i++)); do
  echo $i
done

# iterate over a range
for i in {1..10}; do
  echo $i
done

Arrays

create a script that defines an array of animals and prints:

Number of animals: _
Second animal: _
All animals: _
All animals having removed the second animal: _

Answer

#!/bin/bash

Animals=('dog' 'cat' 'sheep' 'elephant')

echo "Number of animals: ${#Animals[@]}"
echo "Second animal: ${Animals[1]}"
echo "All animals: " "${Animals[@]}"
unset Animals[1]
echo "All animals having removed the second animal: " "${Animals[@]}"

Dictionaries aka Associative Arrays (BASH 4+ only)

create a script that creates a dictionary of different music genres and an example musician. Then print out your dictionary. For more info on declare see bash declare

Answer

#! /usr/bin/env bash
# I've used /usr/bin/env bash here to use the latest downloaded version of bash that I have installed and set as my SHELL of choice in MacOS

declare -A genres

genres[blues]="B.B. King"
genres[hiphop]="Snoop Dogg"
genres[punk]="Sex Pistols"
genres[pop]="Britney Spears"

echo "${genres[@]}"

Conditionals

create a script that prints out whether a string is empty or not. For bonus points, takes this as a command argument. See Bash Conditional Expressions

Answer

#!/bin/bash

string=$1

if [[ -z "$string" ]]; then
  echo "the string is empty"
else
  echo "the string $string is not empty, duh"
fi

File Conditionals

create a script that prints out whether a file exists or not. For bonus points, takes this as a command argument and confirm it's set. See Bash Conditional Expressions

Answer

#!/bin/bash

file=$1

if [[ -z "$file" ]]; then
  echo "you must input a file name as an argument: ./fileExists.bash FILE"
fi

if [[ -f $file ]]; then
  echo "file $file exists!"
else
  echo "file $file does not exist"
fi

Functions

create a function that takes an argument and prints it as part of a sentence.

Answer

#!/bin/bash

helloFunc () {
  echo "You have my attention, $1"
}

helloFunc "do I have yours?"

Handling Signals

create a script that traps a SIGINT and prints a message instead. Be sure to also print your PID or press ctrl-T to get the PID of a running process You can then kill the process like so: kill PID

Answer

echo $$
while true; do
  trap 'echo "SIGINT caught!"' SIGINT
done