Wilcards&Arithmetics

#ysap #bashwildcards

Wildcards are used in Bash for pattern-matching search.

The three main wildcard characters are:

• Star or Asterisk ( * ) matches one or more occurrences of any character, including no character.
• Question mark (?) represents or matches a single occurrence of any character.
• Square brackets ([]) matches any occurrence of character enclosed in the square brackets. It is possible to use different types of characters (alphanumeric characters): numbers, letters, other special characters etc.

Arithmetic Operators

Arithmetic.sh

#!/bin/bash

increase=1 
decrease=1 
echo "Addition: 10 + 10 = $((10 + 10))" 
cho "Subtraction: 10 - 10 = $((10 - 10))" 
echo "Multiplication: 10 * 10 = $((10 * 10))" 
echo "Division: 10 / 10 = $((10 / 10))" 
echo "Modulus: 10 % 4 = $((10 % 4))" ((increase++)) 

echo "Increase Variable: $increase" ((decrease--)) 
echo "Decrease Variable: $decrease"

The output of this script looks like this:

#!/bin/bash

sosoBoy@htb[/htb]$ ./Arithmetic.sh 
Addition: 10 + 10 = 20 
Subtraction: 10 - 10 = 0 
Multiplication: 10 * 10 = 100
Division: 10 / 10 = 1 
Modulus: 10 % 4 = 2 
Increase Variable: 2 
Decrease Variable: 0

We can also calculate the length of the variable. Using this function ${#variable}, every character gets counted, and we get the total number of characters in the variable.

VarLength.sh

htb="HackTheBox"
echo ${#htb}

sosoBoy@htb[/htb]$ ./VarLength.sh
10

Example of script:

• Action: Iterates through every IP address stored in the variable $cidr_ips.
• Context: $cidr_ips is assumed to be a list of IP addresses generated earlier in the script (likely from a CIDR range, to be reviewed).
• Variable: In each iteration, the current IP address is assigned to the variable $host

Inner loop:

• ping: Sends network packets to test connectivity.
• -c 2: Sends exactly 2 packets (count) and then stops.
• $host: The target IP address.
• > /dev/null 2>&1: Suppresses all output.
  > /dev/null: Discards standard output (the normal ping results).
  2>&1: Redirects standard error (error messages) to the same place as standard output (which is discarded).