Linux_Shell-Hacker_Rank

This repo has a Hacker Rank Problem solution and a basic tutorial on Bash.

Uses of echo

echo is used to print the contents of a variable or a string.

echo "Hello World"

Uses of printf

printf is used to print the contents of a variable or a string.

printf "Hello World"

Uses of read read is used to read the contents of a variable or a string.

read -p "Enter your name: " name
echo "Hello $name"

Uses of cat

cat is used to print the contents of a file.

cat README.md

Uses of tr

tr is used to translate the contents of a file.

tr 'a-z' 'A-Z' < README.md

Uses of paste

paste is used to print the contents of a file.

paste README.md

Uses of of if else statements.

if else statements are used to execute a block of code if a certain condition is true.

if [ $a -gt $b ]; then
    echo "a is greater than b"
else
    echo "a is not greater than b"
fi

Uses of of for loops.

for loops are used to iterate over a list of values. Say we have a list of numbers, we can use a for loop to iterate over the list and print each number.

for i in {1..10}
do
    echo "Number is $i"
done

Uses of of while loops.

while loops are used to execute a block of code as long as a certain condition is true.

while [ $a -lt 10 ]
do
    echo "Number is $a"
    a=`expr $a + 1`
done

Uses of of until loops.

until loops are used to execute a block of code as long as a certain condition is false. until [ $a -gt 10 ]

until [ $a -gt 10 ]
do
    echo "Number is $a"
    a=`expr $a + 1`
done

Uses of of case statements.

case statements are used to execute a block of code based on the value of a variable.

case $a in
    1) echo "a is 1";;
    2) echo "a is 2";;
    3) echo "a is 3";;
    4) echo "a is 4";;
    5) echo "a is 5";;
    6) echo "a is 6";;
    7) echo "a is 7";;
    8) echo "a is 8";;
    9) echo "a is 9";;
    10) echo "a is 10";;
    *) echo "a is not between 1 and 10";;
esac

Uses of of functions.

Functions are used to group a block of code together and to reuse the code.

function myfunc() {
    echo "Hello World"
}
myfunc

Uses of of arrays.

array=(1 2 3 4 5 6 7 8 9 10)
echo ${array[0]}
echo ${array[1]}
echo ${array[2]}
echo ${array[3]}
echo ${array[4]}
echo ${array[5]}
echo ${array[6]}
echo ${array[7]}
echo ${array[8]}
echo ${array[9]}

Uses of of associative arrays.

Associative arrays are used to store key value pairs.The key is the index and the value is the value.

declare -A assoc_array
assoc_array[key1]=value1
assoc_array[key2]=value2
assoc_array[key3]=value3
echo ${assoc_array[key1]}
echo ${assoc_array[key2]}
echo ${assoc_array[key3]}

Uses of of functions.

Functions are used to group a block of code together and to reuse the code.

function myfunc() {
    echo "Hello World"
}
myfunc

Uses of Head

Head is used to print the first n lines of a file.

```
head -n 5 README.md
```

Uses of Tail

Tail is used to print the last n lines of a file.

```
tail -n 5 README.md
```

Uses of of grep

grep is used to search for a pattern in a file.

grep "Hello" README.md

Uses of of cut

cut is used to extract a specific field from a file.

cut -d " " -f 1 README.md

Uses of of sort

sort is used to sort a file.

sort -n README.md

Uses of of uniq

uniq is used to remove duplicate lines from a file.

uniq README.md

Uses of of wc

wc is used to count the number of lines, words and characters in a file.

wc README.md

Uses of of tr

tr is used to translate characters in a file.

tr " " "-" README.md

Uses of of sed

sed is used to edit a file.

sed "s/Hello/Hi/g" README.md

Data Types in Shell

Data Types:

Type	Description	Example	Size(bytes)
String	A string is a sequence of characters.	"Hello World"	11
Integer	An integer is a number without decimal points.	123	4
Float	A float is a number with decimal points.	1.23	4
Boolean	A boolean is a true or false value.	true	1
Array	An array is a list of values.	[1, 2, 3, 4, 5]	5
Associative Array	An associative array is a list of key value pairs.	{"key1": "value1", "key2": "value2"}	2
Function	A function is a block of code that can be called.	function myfunc() { echo "Hello World"; }	1

Example:

int=123
float=1.23
printf "Integer: %d\n" $int
printf "Float: %f\n" $float

Bash Arithmetic Operators

In Bash, arithmetic operators are used to perform mathematical operations on numbers. Here are some of the most common arithmetic operators in Bash:

Operator	Description	Example
+	Addition	echo $((2 + 3))
-	Subtraction	echo $((5 - 2))
*	Multiplication	echo $((2 * 3))
/	Division	echo $((6 / 2))
%	Modulus	echo $((7 % 3))
++	Increment	x=5; echo $((x++))
--	Decrement	x=5; echo $((x--))

Note that arithmetic operators are usually used in conjunction with the $(( )) syntax to evaluate the expression as a mathematical operation. For example:

Backslash Escape Sequences in Bash

In Bash, backslash escape sequences are used to insert special characters into strings. Here are some of the most common backslash escape sequences in Bash:

Sequence	Description	Example
\n	Newline	echo -e "Hello\nworld"
\t	Tab	echo -e "Name\tAge"
\\	Backslash	echo "This is a backslash: \\"
\"	Double quote	echo "She said, \"Hello.\""
\$	Dollar sign	echo "The price is \$10."

Note that backslash escape sequences are usually used in conjunction with the -e option in the echo command to interpret the escape sequences. For example:

Common ls Options

Option	Description
-a	Show hidden files and directories
-l	List files in long format
-h	When used with -l, display file sizes in human-readable format
-r	Reverse the order of the list
-t	Sort the list by modification time
-S	Sort the list by file size
-R	List subdirectories recursively
-G	Colorize the output
-1	Display each file on a separate line

Uses of of declare

declare is used to create a variable.

declare -i int
declare -f func
declare -a array
declare -A assoc_array

Type of shell :

1. Bash
2. Zsh

Them are both interpreted by the shell and executed by the shell. The difference is that the Bash shell is a shell that is written in the Bourne Again Shell (BASH) language, while the Zsh shell is a shell that is written in the Zsh language. The Bash shell is the default shell on most UNIX systems, while the Zsh shell is the default shell on most UNIX systems.

We show here shell scripting in the following example or bash programming. However, the same can be done in the Zsh shell. Window command prompt has also has the programming language feature. You can use loops, if else statements, functions, arrays, associative arrays, and more. Its call batch scripting.