end of day 5 week 1

week 1/day 5/day5.md

@@ -0,0 +1,11 @@
+
+if the number of user dobules
+
+the time of execution will be multiply by 2
+
+
+$$
+T(n, m) = n \times m
+T(2n, m) = 2 \times n \times m
+Big-O: O(n·m)
+$$

week 1/day 5/exo1.sh

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+#!/bin/bash
+
+read -p "please enter a number : " number
+
+if [[ -z $number ]]; then
+    echo "you must enter a number"
+    exit
+fi
+
+if (( $number % 2 == 0 )); then
+    echo "Even"
+else
+    echo "Odd"
+fi

week 1/day 5/exo2.sh

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+#!/bin/bash
+
+read -p "please enter a phrase: " text
+
+if [[ -z "$text" ]]; then
+    echo "please enter a string"
+    exit
+fi
+
+count=0
+
+for ((i=0; i<${#text}; i++)); do
+    char="${text:i:1}"
+    if [[ "$char" =~ [A-Za-z]]]; then
+        count++
+    fi
+done
+
+echo "Your string contain $count letter"

week 1/day 5/exo3.sh

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+#!/bin/bash
+
+read -p "Please enter your username: " username
+
+if [[ -z "$username" ]]; then
+    echo "You must enter a username"
+    exit 1
+fi
+
+badChar=false
+
+for ((i=0; i<${#username}; i++)); do
+    char="${username:i:1}"
+    if ! [[ "$char" =~ [A-Za-z] ]]; then
+        badChar=true
+        break
+    fi
+done
+
+firstChar="${username:0:1}"
+validFirstLetter=false
+
+if [[ "$firstChar" =~ [A-Za-z] ]]; then
+    validFirstLetter=true
+fi
+
+if ! $badChar && (( ${#username} <= 20 )) && $validFirstLetter; then
+    echo "The username $username is valid"
+else
+    echo "The username is not valid"
+fi

week 1/day 5/exo4.sh

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+#!/bin/bash
+
+users=("admin" "root1" "John_Doe" "Alice" "Bob42")
+
+badChar=false
+
+for username in "${users[@]}"; do
+
+    badChar=false
+
+    for ((i=0; i<${#username}; i++)); do
+        char="${username:i:1}"
+        if ! [[ "$char" =~ [A-Za-z] ]]; then
+            badChar=true
+            break
+        fi
+    done
+
+    firstChar="${username:0:1}"
+    validFirstLetter=false
+
+    if [[ "$firstChar" =~ [A-Za-z] ]]; then
+        validFirstLetter=true
+    fi
+
+    if ! $badChar && (( ${#username} <= 20 )) && $validFirstLetter; then
+        echo "The username $username is valid"
+    else
+        echo "The username $username is not valid"
+    fi
+
+done
+

week 1/day 5/readme.md

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+# 📘 Week 1 · Day 5 — Bash Exercises
+
+This README documents **all exercises for Week 1 Day 5**, focused on **Bash scripting for Linux system administration and security workflows**.
+
+The exercises mirror the logic implemented previously in **C, Python, SQL, and PowerShell**, reinforcing algorithmic thinking while introducing **Unix shell syntax, conditionals, loops, and defensive scripting**.
+
+---
+
+## 🎯 Learning Objectives
+
+By completing today’s exercises, you will:
+
+* Use Bash variables and user input (`read`)
+* Apply conditional logic with `if / elif / else`
+* Loop over strings and arrays using `for`
+* Perform character validation using regex
+* Implement secure input validation logic
+* Analyze algorithm runtime and scalability
+* Gain confidence writing Linux automation scripts
+
+---
+
+## 🛠 Exercises Overview
+
+### 🧪 Exercise 1 — Even / Odd Number Checker
+
+**Task:**
+
+* Prompt the user for a number
+* Determine whether the number is `Even` or `Odd`
+
+**Concepts practiced:**
+
+* Numeric input handling
+* Arithmetic expressions: `(( ))`
+* Conditional branching
+
+---
+
+### 🧪 Exercise 2 — Count Letters in a String
+
+**Task:**
+
+* Prompt the user for a string
+* Count **letters only** (`A–Z`, `a–z`)
+* Ignore spaces, digits, and special characters
+
+**Concepts practiced:**
+
+* Looping over string characters
+* Regex matching using `[[ =~ ]]`
+* Counter variables
+
+---
+
+### 🧪 Exercise 3 — Username Validator (Single User)
+
+**Task:**
+Validate a username using these rules:
+
+* Length ≤ 20 characters
+* Starts with a letter
+* Contains letters only
+* No digits
+* No spaces
+
+**Output:**
+
+* `Accepted` or `Refused`
+
+**Concepts practiced:**
+
+* Defensive input validation
+* Early exit with `break`
+* String length checking
+* First-character validation
+
+---
+
+### 🧪 Exercise 4 — Validate Multiple Usernames
+
+**Input:**
+
+```bash
+users=("admin" "root1" "John_Doe" "Alice" "Bob42")
+```
+
+**Task:**
+
+* Loop through each username
+* Apply the same validation rules as Exercise 3
+* Print whether each username is valid or invalid
+
+**Concepts practiced:**
+
+* Array iteration
+* Nested loops
+* Reusable validation logic
+
+---
+
+### 🧪 Exercise 5 — Algorithm Analysis (Written)
+
+**Task:**
+Explain what happens to execution time if the number of usernames doubles.
+
+Use:
+
+* `n` = number of usernames
+* `m` = average username length
+
+**Expected result:**
+
+```
+T(n, m) = n × m
+T(2n, m) = 2 × n × m
+Big-O: O(n·m)
+```
+
+---
+
+## 🔐 Security & Sysadmin Perspective
+
+These exercises reflect real-world Bash usage in:
+
+* Linux user management
+* Input validation scripts
+* SSH and access control automation
+* Log parsing and monitoring
+* Security audits and recon scripts
+
+Strong validation and predictable runtime are critical for **secure and reliable system scripts**.
+
+---
+
+## ✅ Completion Criteria
+
+Day 5 is complete when:
+
+* Exercises 1–4 run correctly in Bash
+* Exercise 5 clearly explains runtime scaling
+* Scripts follow safe Bash practices (`[[ ]]`, quoting, defensive checks)
+
+---
+
+## 🔜 Next Step
+
+After Day 5, Week 1 concludes.
+
+Upcoming:
+
+* **Week 2:** Data Structures (arrays, maps, sets)
+* Stronger algorithm focus
+* More security-oriented scripting examples
+
+---
+
+📌 *This README serves as a reference and checklist for Week 1 Day 5 Bash exercises.*