Over the years I have faced several linux challenges that I have solved by googling or thanks to beautiful people who have shared their knowledge. This is a brief compilation of useful tricks grouped in different categories: Files management, searching, bash scripting, networking, compressed files management, packet management, server information and miscellaneous. 📝📁Files management Delete Delete first line: sed -i '1d' file.txt Delete all empty lines: sed '/^$/d' file.txt Delete first two characters from each line: cat file.txt | sed 's/^..//' Delete comments and empty lines: sed '/ *#/d; /^$/d' file.txt Delete carriage return \r: cat input.txt|tr -d "\r" > output.txt Replace Replace with string1 string2 sed -d 's/string1/string2/g' file.txt Replace space by : - sed ':a;N;$!ba;s/\n/\'\'\-\'/g'' Replace replace line break with space: sed ':a;N;$!ba;s/\n/ /g' Add Add at the beginning of the line - sed -d s/^/\-/ file.txt Add at the end of the line - sed -d s/$/\-/ file.txt Filter Filter lines starting with a number: cat file.txt |grep ^[0-9] Filter multiple words: grep -E 'string1|string2' file.txt Filter multiple words old shells: grep -e 'string1' -e 'string2' file.txt Print the third and tenth words from file: cat file.txt | awk '{print $3,$10}' Print the third word from file separated by : - cat file.txt| awk -F"-" '{print $3}' Misc Split a large file every 2000 lines: split -l 2000 input.txt output.txt View  only the lines that contain string1 : sed -n '/string1/p' files.txt Convert lowercase to uppercase: cat file.txt | tr '[:lower:]' '[:upper:] ' Copy permissions from a reference file: chmod --reference=reference_file new_file Copy ownership from a reference file: chown --reference=reference_file new_file 🧮 Let's count Files on the directory: ls | wc -l Lines in a file: wc -l file.txt Words in a file: wc -s file.txt Length of the longest line in a file: wc -L file.txt Number of files and directories in a directory: tree -a 🔍Searching Files less than two days old find -mtime -2 Files older than 5 days: find -mtime +5 Files created today: find ./ -type f -daystart -ctime -1 Directory by name: find / -type d -name directory_name Find files by content: find ./ -type f -exec grep -H ' content ' {} \; 👨‍💻👩‍💻Bash scripting basics For syntax #!/bin/bash for i in `seq 1 90` do echo $i done Execution: ./read_file_line_per_line.sh file_to_read.txt Read file line per line #!/bin/bash while IFS='' read -r line || [[ -n "$line" ]]; do echo "Text read from file: $line" done < "$1" Execution: ./read_file_line_per_line.sh file_to_read.txt Read file word per word #!/bin/bash while IFS='' read -r line || [[ -n "$line" ]]; do for word in $line do echo $word done done < "$1" Check if a file exists #!/bin/bash if [ -f $path/to/file.txt ];  then echo "exist" else echo "no exist" fi Check ip reachability #!/bin/bash ping -w1 -c3 $IP >/dev/null 2>&1 && echo "ON" || echo "OFF" 🌐Networking Ping from a defined interface: ping -I interface_name ip Rename interface: link set current_name name new_name Show IP addresses without infconfig : ip address show Traffic Traffic capture with tshark: tshark -i interface_name .151 -f "host ip and port port_number " Traffic capture with tcpdump: tcpdump -i interface_name dst port port port_number -w capture.pcap Store traffic output: tcpdump -ni eth0 -w capture.pcap Read traffic capture form the CLI: tcpdump -ttttnnr capture.pcap 👀 Port scanning Check if 5050 port is open: nc -zvn ip 5050 Check if 5050 and 5055 are open: nc -zvn ip 5050 5055 Check if range of ports: nc -zvn ip 5050-5055 Connect to on port 5050 and send content of input.in: ip nc ip 5050 < input.in 👂👂 Listening Listen for TCP connections on port 5050: netcat -l 5050 Listen for UDP connections on port 5050: netcat -ul 5050 Listen for TCP connections on port 5050 and store data received in to "received.txt": netcat -l 5050 > received.txt Listen for TCP connections on port 5050 and continue listening after client has disconnected: netcat -k -l 5050 🗃️ Compressed files management : Decompress: .tar.gz files Compress tar -czvf compressed.tar.gz /direcory/to/compress/ tar -xzvf compressed.tar.gz : Decompress: .tar files Compress tar -cvf compressed.tar /direcory/to/compress/ tar -xvf compressed.tar : Decompress: .gz files Compress gzip file.txt gzip -d file.txt.gz : Decompress: .zip files Compress zip compressed.zip /direcory/to/compress/ unzip compressed.zip 🎉 Read compressed file without decompress: Filter compressed file without decompress: Split compressed file in parts of 10m size: Bonus zcat compressed.gz zgrep -n string compressed.gz split -b 10m file.tar.gz "file.tar.gz.part" 📦Packet management (YUM and DNF) What provides a package yum whatprovides package_name dnf provides package_name Package description: yum info package_name dnf info package_name Update security  packages: yum update --security dnf update --security List dependencies from a package example httpd: yum deplist httpd dnf repoquery --deplist httpd Download all packages and dependencies needed to install something, example FTP: yumdownloader --resolve FTP dnfdownload --resolve FTP Remove orphan packages: and and package-cleanup --orphans package-cleanup --oldkernels dnf list extras dnf remove $( dnf repoquery --installonly --latest-limit -1 -q ) List pending security updates: yum list-security dnf updateinfo list --security ℹ️Server info Number of processors: grep processor /proc/cpuinfo | wc -l Number of cores: dmidecode -t processor | grep "Core Count" Number of enabled cores: dmidecode -t processor | grep "Core Enabled" RAM memory: free -m | head -2 | tail -1 | awk {'print $4'} Free space: df -h | awk {'print $3'} | head -3 | tail -1 Release version: cat /etc/*release* 🍕 Misc Execute a command as another user: sudo -u user command Clean cache: echo 3 > /proc/sys/vm/drop_caches Create symbolic link: ln -s /file_or_directory_path /direct_access_path Create FIFO files: mkfifo filename Know more information about and image from CLI: identify -verbose image.png Pretty print json files in CLI: cat file.json | jq Print only values of the key my_key from json file: jq '.[] | .my_key' file.json Hope this was useful for you. If you want more don't hesitate visit my github

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