+ touch hello.txt --to make file
+ mkdir ---to make directory
+ ls -l --detail of file | ls cp in bin will show availablity
+ cp -r file1(source) file2(destination) --copy folder/files
+ mv file1(source) file2(destination) --rename/move files
+ rmdir filename/ rm -r filename ---to remove directory(shift delete similar for rm command)
diff --git a/2026/day-03/linux-commands-cheatsheet.md b/2026/day-03/linux-commands-cheatsheet.md new file mode 100644 index 0000000000..b9cce1bf72 --- /dev/null +++ b/2026/day-03/linux-commands-cheatsheet.md @@ -0,0 +1,94 @@ +# Process Management +systemd is the 1st process
+systemctl status nginx/docker --to check status of process
+systemctl start nginx/docker --- To start any process
+systemctl stop nginx/docker --- To Stop any process
+journalctl -u nginx/docker ---- to show all logs of an individual process
+ +# User Management +whoami ---- shoes which user is active
+sudo adduser xxx --- Adds user and made directory automatically
+sudo passwd xxx --- set up password for login
+su xxx --- command to enter inside user giving password (opens black bash)
+which bash --- which bash currently am i using (usually coloured) gives path
+sudo useradd -m yyy -s usr/bin/bash --- to make bash similar to **older coloured style** and using -m (Simialr to windows switching)
+cd / > cd home --- ls -l gives list of all users
+cat /etc/group --- shows all the user group
+sudo addgroup ggg ---making group for user
+sudo gpasswd -a xxx ggg ---adding user inside group. here xxx is added in group ggg along **with permission** gets added
+sudo gpasswd -d xxx ggg ---To remove the user from that group and revoke their permissions. Restart with newgrp current user
+sudo usermod -aG docker ubuntu ---Adding an Ubuntu User to the docker Group to **avoid sudo** and have permissions
+sudo chown ggg filename.txt ---change the individual owner of the file from ubuntu to other user only valid for individual
+sudo chgrp xxx filename.txt --change group owner can be done with chown (:) as well
+# File System +Read (cat)
+Write (vim/nano)
+Execute (shell/ ./)
+mkdir -p devops -----makes directory **with path** without error even if it exists do not throw error
+vim hello.txt > Insert i > write content > Esc > :wq(save and quit)/:q!(exit without saving)
+newgrp ubuntu --- changes current active primary group to the group named ubuntu for your current terminal session
+-rwxrwxrwx --read write execute for **owner group others** in sets of 3
+chmod 777 ---giving all permission / chmod 400 ----giving only read permission
+ +# Volume Mounting +lsblk ---volume/disk all attached to the server shows block with various partition
+xvda ---extended version is written in form **/dev/xvda**
+df -h ---free disk space in disk and shows mount point
+Attach and Mount are 2 different thing. /dev/xvda shows attachment to system
+Instance attached to volume is called attaching. Binding volume to a location is called mounting.
+EBS(Elastic block store to to create ssd) ---go to EBS in aws and create multiple volumes.
+select volume > Actions > Attach volume to the corrosponding instances(select correct device name) > Check through lsblk
+To make volume of EBS into useable volume convert into Physical Volume
+Logical volume size can be incraesed or decreased according to the usage
+ + LVM(Logical Volume Manager) + ------------Logical Volume----------------------- + -------- --------- ---------- + | 10GB | | 6GB | | | + --------- ---------- ----------- + | | | + | | | + ------------------------------------------------------ + | Volume Group | + | | + ------------------------------------------------------- + | | | + | | | + -------- --------- ---------- + | 10G | | 12G | | 11 GB | + --------- ---------- ----------- + --------------Physical volume------------------- + +# Logical Volume Manager (LVM) +Sudo lvm ---become a root user initially. Its a tool to manage LVM having commands for mounting
+pvcreate /dev/xvdf /dev/xvdg /dev/xvdh ----create physical volume for 3 ebs volume available in aws
+pvs ---- shows the physical volume details
+ +vgcreate tws_vg /dev/xvdf /dev/xvdg ---To create Volume group using 2 physical volume earlier made. initail is the vg nam and then from the source path to be combined
+vgs ----shows list of all the volume from group craeted where PV is phy. vol. and LV is Logical vol.
+ +lvcreate -L 10G -n tws_lv tws_vg --- to create logical volume from the volumegroup
+lvs --- shows list of all the volume of group created
+ +pvdisplay ---- to display physical volume details
+vgdisplay ----- to display volume group details
+lvdisplay ---- to displaylogical volume details
+ +# How to mount volumes +Go to root always
+mkdir /mnt/tws_lv_mount --- create a temproary directory which creates a location where volume is mounted
+mkfs.ext4 /dev/tws_vg/tws_lv ---to format the path and create space and make file system
+mount /dev/tws_vg/tws_lv /mnt/tws_lv_mount --mount the logical volume to specified location craeted before to bind the path
+umount /mnt/tws_lv_mount ---to unmount the volume directory
+Now you can use the path to craete directory and work here /mnt/tws_lv_mount
+ +# Directly mount physical volume to disk mount +No need to go to room
+mkdir /mnt/tws_disk_mount ----this is to create space for disk mount directly from phy. vol.
+mkfs -t ext4 /dev/xvdh ----file system to mount disk store
+mount /dev/xvdh /mnt/tws_disk_mount --- mounting disk to the destination
+df -h --to check all the disk mounted
+ +# Dynamic storage management with EBS(AWS) +Adding extra storage to Logical Volume
+lvm > lvextend -L +5G -n /dev/tws_vg/tws_lv
diff --git a/2026/day-04/linux-practice.md b/2026/day-04/linux-practice.md new file mode 100644 index 0000000000..f8a8357559 --- /dev/null +++ b/2026/day-04/linux-practice.md @@ -0,0 +1,36 @@ +Systemctl status ssh/docker --- to see the curreent status of a single process
+
+
+
+htop -- to see the running status of the process and track live running process
+
+kill -9 PID --force kill the running process
+kill PID --kill the process
+
+systemctl list-units --state=failed
+systemctl list-units --state=waiting
+
+
+
+
+pgrep nginx --- Searches for processes by name and returns their Process IDs (PIDs)
+
+lsb_release -a (The Legacy Standard) --- prints all available Linux Standard Base (LSB) and **distribution-specific** version details
+cat /etc/os-release (The Modern Standard) --- tells you about the specific **Linux distribution** (OS) and its version
+
+cp /etc/hosts /tmp/runbook-demo/hosts-copy && ls -l /tmp/runbook-demo --copy directory file from hosts to copy hosts and dispalys permission
+
+
+ps -o pid,pcpu,pmem,comm -p
+ pcpu --- details about cpu pmem --- detail about memory
+ comm --- short executable command -p
+ free -h --- shows free space in human redeable format. without -h it is in byte format
+
+du -sh /var/log --- calculates and displays the total disk space used by the /var/log folder in redeable format number
+iostat --- Focuses heavily on storage drive performance and input/output (I/O) speeds and idle time
+vmstat --- Focuses heavily on virtual memory, RAM, paging, processes, and CPU activity(Virtual Memory Statistics)
+dstat --- Combines both tools into a single, Everything simultaneously—CPU, disk, network, and memory(Versatile Statistics)
+
+
+
+curl -I API ---- checks application-layer web responses using HTTP(give full address) (Is the web application/API running and healthy?)
+
+tail -n 5 /var/log/syslog --- last 5 lines of a particular log files
+
+Phase 1: Initial Triage & VerificationVerify OS Environment: Run cat /etc/os-release to confirm the distribution baseline.
+Test Network Reachability: Run ping
+Inspect HTTP Headers: Run curl -I http://localhost to capture the exact status code (e.g., 502 Bad Gateway).
+Audit Open Ports: Run sudo ss -tulpn to ensure Nginx is actively listening on ports 80/443. + +Phase 2: Elevate Verbosity (The "If This Worsens" Plan)
+Open Configuration: Run sudo nano /etc/nginx/nginx.conf (Do not use cd). +Enable Debug Logs: Locate the error_log directive and append debug to the end of the line:**nginxerror_log /var/log/nginx/error.log debug**
+Test Layout Syntax: sudo nginx -t ---- to verify there are no missing semicolons or typos.
+Apply Changes Safely: sudo systemctl reload nginx --- to load the settings without dropping user traffic.
+Stream Live Errors: sudo tail -f /var/log/nginx/error.log --- to watch the debug output in real time. + +Phase 3: Advanced Diagnostics & RecoveryTrace System Calls: Run sudo strace -fp
+echo "Line 1" > notes.txt -----add content to the line and over write if anything written
+echo "Line 2" >> notes.txt ----add content and append the content at the end it do not overwrite
+echo "Line 3" | tee -a notes.txt ---display the content as well as append at last. If -a not there it will overwrite
+cat notes.txt ---displayes the overall output +head -n 2 notes.txt ---diaplays firat 2 line
+tail -n 2 notes.txt ---displays last 2 lines
+
+echo "Line 2" >> notes.txt ----add content and append the content at the end it do not overwrite
+echo "Line 3" | tee notes.txt ---display the content as well as append at last. If -a not there it will overwrite
+
+ / > ls -l ---you get bin sbin called directories binaries and system binaries
+ /user/bin > ls --shows all the linux command
+ /bin --- Essential command binaries all the commands are either on bin and system command is in sbin
+ /user/
+ /opt --- Optional/third-party applications
+ + /var/log - **Log files** -- all log files and can open through vim
+
+ -- 2>dev/null ---its a black hole where all eoor goes for example permission denied + + Find the largest log file in /var/log. Use of log file scenario +du -sh /var/log/* 2>/dev/null | sort -h | tail -n 5 --sort and gives result of last 5 files
+
+
+cat /etc/hostname ---displays the unique network name assigned to your Linux system
+ +Check your home directory +ls -la ~ ---list aal hidden file but ~ is used to access home directory from anywhere + +# Scenario 1 + systemctl status myapp ----Check the status of myapp
+ systemctl is-enabled myapp --is system enabled
+ sudo journalid -u myapp -e --no-pager --check the log file in chronological order
+ sudo ss -tulpn -- Check other service (like Apache or Nginx) already grabbed the port myapp needs
+ + # Scenario 2 + htop --to see memory usage + ps aux --sort=-pcpu | head -n 5 -- (-pcpu) arrange in decending and apply head or remove minus and apply tail
+ + # Scenario 3 + systemctl status docker ---status of docker
+ journalctl -u docker -n 50 ---chek log file
+ journalctl -u docker -f --follow log in real time
+ + # Scenario 4 + ls -l home/user/backup.sh --to check the permission
+ chmod a+x home/user/backup.sh --gives permission to execute to all
+ ls -l home/user/backup.sh --verify all cmd has r-xr-xr-x permission
+ (or) chmod 755 will work --based on number system but it has all the group
+ + diff --git a/2026/day-08/day-08-cloud-deployment.md b/2026/day-08/day-08-cloud-deployment.md new file mode 100644 index 0000000000..c024e67993 --- /dev/null +++ b/2026/day-08/day-08-cloud-deployment.md @@ -0,0 +1,18 @@ +# Part 1: Launch Cloud Instance & SSH Access +Step 1: Create a Cloud Instance
+Step 2: Connect via SSH
+ +# Part 2: Install Docker & Nginx + Step 1: Update System --- sudo apt update
+ Step 3: Install Nginx -- sudo apt-get install nginx
+ Verify Nginx is running: -- systemctl status nginx
+ + # Part 3: Security Group Configuration + http://51.21.160.162/ +
+ tail -f /var/log/nginx/access.log
+Step 2: Save Logs to File(~ home) --- cp -r error.log ~/nginx.txt
+Step 3: Download Log File to Your Local Machine --- scp -i shell-scripting.pem ubuntu@51.21.160.162:~/nginx.txt .
diff --git a/2026/day-09/day-09-user-management.md b/2026/day-09/day-09-user-management.md new file mode 100644 index 0000000000..7e79fa7a67 --- /dev/null +++ b/2026/day-09/day-09-user-management.md @@ -0,0 +1,49 @@ +# Task 1: Create Users +sudo adduser professor (password & details automatically asked)
+sudo adduser tokyo
+sudo useradd -m berlin -s usr/bin/bash ---craeteonly user name
+sudo passwd berlin ---to create password + +# Task 2: Create Groups +Create group named developers ----sudo addgroup developers +Create group named admins --- sudo addgroup admins + +# Task 3: Assign to Groups +sudo usermod -aG developers tokyo --tokyo → developers
+sudo usermod -aG developers,admins berlin ---berlin → developers + admins (both groups)
+sudo gpasswd -a professor admins --- professor → admins
+Check group after each step --- cat /etc/group
+ +# Task 4: Shared Directory +sudo mkdir -p /opt/dev-project ---Create directory: /opt/dev-project
+sudo chown :developers /opt/dev-project ----change owner to developer
+sudo chmod 775 /opt/dev-project/ --chnage permission
+
+berlin@ip-172-31-43-101:/opt/dev-project$ touch berlin.txt --creates file
+ +cd /opt/dev-project >>> su tokyo --file created inside
+tokyo@ip-172-31-43-101:/opt/dev-project$ touch tokyo.txt
+ +#Testing negative scenario +This happened because owner is changed to developer so dev has tokyo and berlin added not professor +cd /opt/dev-project >>> su professor user enters
+
+sudo usermod -aG project-team niarobi
+sudo usermod -aG project-team tokyo
+
+
+Test by creating file as nairobi
+
+sudo chown :project-team ubuntu
+sudo chgrp project-team ubuntu
diff --git a/2026/day-10/day-10-file-permissions.md b/2026/day-10/day-10-file-permissions.md new file mode 100644 index 0000000000..e1c3f1fdcd --- /dev/null +++ b/2026/day-10/day-10-file-permissions.md @@ -0,0 +1,26 @@ +# Task 1: Create Files +touch devops.txt --creating file
+touch notes.txt --creating file
+echo "This is devops" > notes.txt --entring data
+echo "This is appending" >> notes.txt --appending data
+vim script.sh --creating script and saving
+
+vim script.sh ---View script.sh in vim read-only mode
+
+
+standard groupadd command can only create one group at a time
+sudo chown -R professor:planners heist-project/ --here -R changes user and group for all files present inside in 1 go
+ diff --git a/2026/day-12/day-12-revision.md b/2026/day-12/day-12-revision.md new file mode 100644 index 0000000000..2aa3717f6e --- /dev/null +++ b/2026/day-12/day-12-revision.md @@ -0,0 +1,29 @@ +# Process Management +systemctl status nginx/docker --to check status of process
+systemctl start nginx/docker --- To start any process
+systemctl stop nginx/docker --- To Stop any process
+journalctl -u nginx/docker ---- to show all logs of an individual process
+ +# User Management +whoami ---- shoes which user is active
+sudo adduser xxx --- Adds user and made directory automatically
+sudo passwd xxx --- set up password for login
+su xxx --- command to enter inside user giving password (opens black bash)
+which bash --- which bash currently am i using (usually coloured) gives path
+sudo useradd -m yyy -s usr/bin/bash --- to make bash similar to **older coloured style** and using -m (Simialr to windows switching)
+cat /etc/group --- shows all the user group
+sudo addgroup ggg ---making group for user
+sudo gpasswd -a xxx ggg ---adding user inside group. here xxx is added in group ggg along **with permission** gets added
+sudo gpasswd -d xxx ggg ---To remove the user from that group and revoke their permissions. Restart with newgrp current user
+sudo usermod -aG docker ubuntu ---Adding an Ubuntu User to the docker Group to **avoid sudo** and have permissions
+sudo chown ggg filename.txt ---change the individual owner of the file from ubuntu to other user only valid for individual
+sudo chgrp xxx filename.txt --change group owner can be done with chown (:) as well
+# File System +Read (cat)
+Write (vim/nano)
+Execute (shell/ ./)
+mkdir -p devops -----makes directory **with path** without error even if it exists do not throw error
+vim hello.txt > Insert i > write content > Esc > :wq(save and quit)/:q!(exit without saving)
+newgrp ubuntu --- changes current active primary group to the group named ubuntu for your current terminal session
+-rwxrwxrwx --read write execute for **owner group others** in sets of 3
+chmod 777 ---giving all permission / chmod 400 ----giving only read permission
diff --git a/2026/day-13/day-13-lvm.md b/2026/day-13/day-13-lvm.md new file mode 100644 index 0000000000..aa1f34e7c2 --- /dev/null +++ b/2026/day-13/day-13-lvm.md @@ -0,0 +1,20 @@ +# Task 1-4 +
+ip addr showIPs ---MAC addresses, connection status, MTU, and interface names. Deep network troubleshooting and checking physical link layer stats.
+ping -c 4 google.com --ping cmd test whether a specific network destination is online and reachable
+
+
+Port Conflict Troubleshooting: If you try to launch a web server and it crashes saying "Port 80 already in use", running ss -tulpn will instantly reveal the exact process name and ID blocking that port.
+
+
+ Analyzing Security & Server Software (Footprinting)
+ Verifying Cache and Content Types - It tells you what kind of file is sitting at the URL via the content-type
+ + +-----------------------+--------------------+---------------------------------------------------+ + +| COMMAND | TROUBLESHOOT LAYER | BEST USED FOR | ++-----------------------+--------------------+---------------------------------------------------+ + +| nc -zv localhost | Transport (TCP) | ANY port (SSH, MySQL, Redis). Just tests if the | +| | | application door is open or closed. | ++-----------------------+--------------------+---------------------------------------------------+ + +| curl -I http:// | Application (HTTP) | ONLY Web/API ports (80, 443, 8080). Tests if the | +| | | web software is responding correctly. | ++-----------------------+--------------------+---------------------------------------------------+ + +
+
+ +### DNS Record Types +* **`A`**: Maps a human-readable domain name directly to an **IPv4** address. +* **`AAAA`**: Maps a human-readable domain name directly to an **IPv6** address. +* **`CNAME`**: Creates an alias that points one domain name to another domain name instead of an IP address. +* **`MX`**: Specifies the mail server responsible for accepting email messages on behalf of the domain name. +* **`NS`**: Identifies the authoritative name servers trusted to hold and manage the DNS records for the domain. + +
+2.Running a script : chmod +x ---gives permission(rwx) , + ./script.sh --cmd to execute bash script.sh---ignore shebang force execution using bash
+3.Comments — single line (#) and inline---- singel line comment
+4.Variables — declaring, using, and quoting ($VAR, "$VAR", '$VAR') +5.declearing variable using $VAR , using same variable "$VAR" , '$VAR' traeating character as literals strings not variable
+6.Reading user input —---read -p "Enter..." VAR : This is way to call from user
+7.Command-line arguments — $0(usually file name), $1(First arg), $#(Number of Arg), $@(dispaly all arg entered by user), $?(exit status of the last executed command)
+ +# Task 2: Operators and Conditionals +1.String comparisons — = strings are equal, != strings are not equal, -z true if string is empty, -n true when string is non empty
+2.Integer comparisons — -eq(equal to), -ne(notn equal to), -lt(les than), -gt(greater than), -le(less than), -ge(greater then equals)
+3.File test operators — -f (true for file), -d(true for directory), -e(true for path), -r(gives read), -w (gives write), -x(execute), -s (file exist)
+4.if []; then, elif []; then, else syntax---of else if +5.Logical operators — && (both are true), ||(one is true), !(logical not) +6.Case statements — case ... esac : cases + +# Task 3: Loops +Document with examples: +1. `for` loop — list-based and C-style + + #Iterating over explicit items +for color in Red Green Blue; do + echo "Color: $color" +done + +#Iterating over a number range {start..end..step} +for i in {1..5..2}; do + echo "Number: $i" +done + +#C Style +for ((i=1; i<=3; i++)); do + echo "Count: $i" +done + +2. `while` loop + count=1 +while [ $count -le 3 ]; do + echo "Value: $count" + ((count++)) # Increment the variable +done + +3. `until` loop + count=1 +until [ $count -gt 3 ]; do + echo "Value: $count" + ((count++)) +done + +4. Loop control — `break`, `continue` + for num in {1..5}; do + if [ $num -eq 2 ]; then + continue # Skip the rest of the code for number 2 + fi + if [ $num -eq 5 ]; then + break # Exit the loop completely when reaching 5 + fi + echo "Number: $num" +done + +5. Looping over files — `for file in *.log` + #Process all log files in the current directory +for file in *.log; do + #Check if files actually exist to avoid running on literal '*.log' + if [ -f "$file" ]; then + echo "Processing file: $file" + fi +done + +6. Looping over command output — `while read line` + + #Reading line-by-line from a command pipeline +df -h | while read -r line; do + echo "Disk info: $line" +done + +#Reading line-by-line directly from a file +while read -r line; do + echo "Line content: $line" +done < input.txt + +# Task 4: Functions +1. Defining a function — function_name() { ... } + #Definition +show_welcome() { + echo "Welcome to the system automation script!" +} + +2. Calling a function + #Call the function defined above + show_welcome + +3. Passing arguments to functions — $1, $2 inside functions + #Define a function that expects two inputs +show_user_info() { + echo "The username is: $1" + echo "The assigned role is: $2" +} + +#Call the function and pass two string arguments +show_user_info "admin_user" "System Administrator" + +4. Return values — return vs echo +#Method 1: Using 'return' for success/failure checks +check_root() { + if [ "$USER" = "root" ]; then + return 0 # Success + else + return 1 # Error/Failure + fi +} + +#Method 2: Using 'echo' to send back actual data strings +calculate_tax() { + local total=$(($1 * 2)) + echo "$total" +} + +#Running Method 1 +check_root +echo "Exit status was: $?" + +#Running Method 2 (Capturing output into a variable) +final_bill=$(calculate_tax 50) +echo "The calculated tax amount is: $final_bill" + +5. Local variables — local + #!/bin/bash + +#A global variable +CITY="Berlin" + +update_location() { + # Local variable: only exists inside this function + local CITY="Paris" + echo "Inside function, CITY is: $CITY" +} + +#Run the function +update_location + +#Check global variable value +echo "Outside function, CITY is still: $CITY" + +Result: +Inside function, CITY is: Paris +Outside function, CITY is still: Berlin + +# Task 5: Text Processing Commands + +1. grep — Search PatternsUsed to search text files for lines matching a specified pattern.
+-i: Ignores character case (matches both error and ERROR).
+-r: Recursively searches all files inside directories and subdirectories.
+-c: Displays only the numerical count of matching lines instead of the text.
+-n: Displays the line number in the file where the match was found.
+-v: Inverts the match, printing only lines that do not match the pattern.
+-E: Enables Extended Regular Expressions (ERE) for complex patterns using | or ?.
+ +2. awk — Field Processing and Patterns +1, $2, $NF: Represents column numbers.
+$NF automatically references the very last column.
+-F: Defines a custom field separator character (defaults to whitespace).
+BEGIN { ... }: Executes commands before any text rows are processed.
+END { ... }: Executes commands after all text rows have been processed.
+ +Example : +#Print the 1st and 3rd columns from a colon-separated file (like /etc/passwd) +awk -F':' '{print $1, $3}' /etc/passwd + +#Print lines where the 3rd column value is greater than 100 +awk '$3 > 100 {print $0}' data.txt + +3. sed — Stream Editor +s/search/replace/g: Substitutes 'search' with 'replace' globally across the line.
+d: Deletes targeted lines matching a pattern or line number.
+-i: Edits the file in-place directly instead of printing output to the terminal screen.
+ +Example : +#Replace 'http' with 'https' globally in a file and save changes directly +sed -i 's/http/https/g' config.txt + +#Delete line 5 from a text file +sed '5d' data.txt + +4. cut — Extract Columns + -d: Sets the custom delimiter character (must be a single character).
+-f: Specifies which fields/columns to extract (e.g., -f1 or -f2,4).
+-c: Extracts specific character positions or ranges instead of columns.
+ +Example : +#Extract the 1st and 2nd columns from a comma-separated CSV file +cut -d',' -f1,2 addresses.csv + +5. sort — Arrange Lines +-n: Sorts values numerically rather than treating them as standard string text.
+-r: Reverses the sorted output order (e.g., descending instead of ascending).
+-u: Outputs only unique matching rows, throwing away exact duplicates.
+ +Example : +#Sort log file numbers numerically in reverse order +sort -nr prices.txt + +6. uniq — Deduplicate and CountFilters or displays duplicate lines from an input source. Note: uniq only detects adjacent duplicate lines, so you must run sort before it.
+-c: Prefixes each unique line with the total number of times it occurred. +-u: Prints only unique lines that never repeat in the file. +-d: Prints only lines that have matching duplicate copies. + +Example : +#Find unique lines and count their occurrences +sort names.txt | uniq -c + +7. tr — Translate or Delete Characters + Transforms, squeezes, or deletes characters from standard input. It does not accept filenames directly as arguments. + -d: Deletes specified target characters from the input text stream entirely.
+ -s: Squeezes repeating identical characters down to a single character instance.
+ +Example: +#Convert all lowercase text to uppercase characters +echo "hello world" | tr 'a-z' 'A-Z' + +#Delete all carriage return characters (\r) from a Windows text file +tr -d '\r' < windows.txt > linux.txt + +8. wc — Word CountCalculates counts for lines, words, and characters inside data.
+ -l: Displays the total line count.-w: Displays the total word count.
+ -c: Displays the total byte/character count.
+ + Example : + #Count how many total lines are present inside a log file + wc -l system.log + +10. head / tail — File InspectionDisplays portions from the beginning or absolute end of text files.
+ -n X: Limits output to exactly X lines (e.g., -n 5 or -n 20).
+ -f: (Tail only) Enters continuous follow mode, printing new log lines onto the screen in real-time as they are written.
+ + Example : + #View the first 5 lines of a configuration file + head -n 5 setup.conf + + #Watch a system log update in real-time as events occur + tail -f /var/log/syslog + +# Task 6: Useful Patterns and One-Liners + +1. Find and Delete Files Older Than 30 Days + + find /var/log/app/ -type f -name "*.log" -mtime +30 -delete + +2. Track Top 5 Error Sources in Real Time (Tail + Filter) + + tail -f /var/log/syslog | grep --line-buffered -i "error" | awk '{print $5, $6}' + +3. Replace a String Across Multiple Files In-Place + + grep -rl "http://old-api.local" ./src/ | xargs sed -i 's|http://old-api.local|https://production.com|g' + +4. Check if a Service is Running (With Action) + + systemctl is-active --quiet nginx || (echo "Nginx down! Restarting..." && systemctl start nginx) + +5. Aggregate and Count HTTP Status Codes from a Log + + awk '{print $9}' /var/log/nginx/access.log | sort | uniq -c | sort -nr + +# Task 7 : Error Handling and Debugging + +1. Exit Codes — $?, exit 0, exit 1 + exit 0: Terminates the script and signals absolute success. + exit 1 (or any value up to 255): Terminates the script and signals a specific error. + + Example : + #!/bin/bash + +TARGET_FILE="/etc/missing_config.conf" + +if [ ! -f "$TARGET_FILE" ]; then + echo "Critical Error: Configuration file missing!" + exit 1 # Stops script immediately, returns status 1 +fi + +echo "File found." +exit 0 # Script finished successfully + +2. set -e — Exit on Error + +#!/bin/bash +set -e + +#If this directory does not exist, the script stops right here +cd /non/existent/directory + +#This line will never execute because of 'set -e' +echo "This message will not print." + +3. set -u — Treat Unset Variables as Error + +#!/bin/bash +set -u + +USER_NAME="Alice" + +#Typo in variable name throws an error and crashes the script safely +echo "Welcome, $USER_NAM" + +4. set -o pipefail — Catch Errors in Pipes + + #!/bin/bash +#Without pipefail, this entire line returns 0 (success) because wc succeeds +#With pipefail, this line returns a non-zero failure because cat fails +set -o pipefail + +cat non_existent_file.txt | wc -l +echo "Pipeline exit status: $?" + +5. set -x — Debug Mode (Trace Execution) ---Prints every command to the terminal screen exactly as it gets executed, with variables fully expanded. + + #!/bin/bash + +#Turn on debugging trace +set -x + +PREFX="Backup" +DATE=$(date +%F) +FILENAME="${PREFX}_${DATE}.tar.gz" + +#Turn off debugging trace +set +x + +echo "Generated: $FILENAME" + +Result : ++ PREFX=Backup +++ date +%F ++ DATE=2026-05-31 ++ FILENAME=Backup_2026-05-31.tar.gz ++ set +x +Generated: Backup_2026-05-31.tar.gz + +6. Trap — trap 'cleanup' EXIT ---Allows you to intercept system signals or script termination. + +#!/bin/bash +set -e + +#Define a cleanup function +cleanup_temp_files() { + echo "Cleaning up temp directory..." + rm -rf "$TEMP_DIR" +} + +#Register the trap: Run the function whenever the script exits +trap cleanup_temp_files EXIT + +#Create a temporary working workspace +TEMP_DIR=$(mktemp -d) +echo "Working in: $TEMP_DIR" + +#Simulate a script failure +ls /invalid/folder/path + +Result : + Working in: /tmp/tmp.jK98dx2Z +ls: cannot access '/invalid/folder/path': No such file or directory +Cleaning up temp directory...