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Bash

Most commands listed here will work on any linux distributions but if in doubt it will most likely run on the latest Ubuntu.

Some great helpers:

Basics

Random basics

  • Show all files: ls -halt
  • Check installed packges: sudo tasksel
  • Update and upgrade: sudo apt update && apt -y full-upgrade && apt -y autoremove
  • Upgrading to a newer release: do-release-upgrade
  • Check who is online: w
  • Show all system users: cut -d: -f1 /etc/passwd
  • Save to file: ls -halt > result.txt
  • Append to file: echo "add this" >> existing-file.txt
  • Pipe output e.g. to trash (to not see it): grep "stuff" 2> /dev/null
  • Change owner of file or dir: chown user:group blah
  • Change owner of file or dir recersive for all folders below: chown -R user:group blah
  • Change file / dir permissions: chmod 600 file

Chain commands:

  • Pipe the output of command1 to command2: <command1> | <command2>
  • Execute command2 after command1: <command1> ; <command2>
  • Execute command2 if command1 succeded: <command1> && <command2>
  • Redirect errors of command1 to file1: <command1> 2> <file1>
  • Redirect standard and error output of command1 to file1 <command1> &> <file1>

Cursor

Command Description
Ctrl+A Jump to beginning.
Ctrl+E Jump to end.
Ctrl+W Delete one word left of the cursor.
Ctrl+U Delete entire line.
Ctrl+Y Paste back what you just deleted.

script snippets

Check if root

if [ "$EUID" -ne 0 ]; then
    echo "You need to run this script as root"
    exit 1
fi

Check path

if [ "$PWD" != "$HOME" ]; then
    echo "You need to run this script from your home directory $HOME"
    exit 1
fi

Check virtualization platform (openvz)

if [ "$(systemd-detect-virt)" == "openvz" ]; then
    echo "OpenVZ is not supported"
    exit
fi

Check virtualization platform (lxc)

if [ "$(systemd-detect-virt)" == "lxc" ]; then
    echo "LXC is not supported."
    exit
fi

Minimal safe Bash script template based this blog:

#!/usr/bin/env bash

set -Eeuo pipefail

cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1

trap cleanup SIGINT SIGTERM ERR EXIT

usage() {
  cat <<EOF
Usage: $(basename "$0") [-h] [-v] [-f] -p param_value arg1 [arg2...]
Script description here.
Available options:
-h, --help      Print this help and exit
-v, --verbose   Print script debug info
-f, --flag      Some flag description
-p, --param     Some param description
EOF
  exit
}

cleanup() {
  trap - SIGINT SIGTERM ERR EXIT
  # script cleanup here
}

setup_colors() {
  if [[ -t 2 ]] && [[ -z "${NO_COLOR-}" ]] && [[ "${TERM-}" != "dumb" ]]; then
    NOCOLOR='\033[0m' RED='\033[0;31m' GREEN='\033[0;32m' ORANGE='\033[0;33m' BLUE='\033[0;34m' PURPLE='\033[0;35m' CYAN='\033[0;36m' YELLOW='\033[1;33m'
  else
    NOCOLOR='' RED='' GREEN='' ORANGE='' BLUE='' PURPLE='' CYAN='' YELLOW=''
  fi
}

msg() {
  echo >&2 -e "${1-}"
}

die() {
  local msg=$1
  local code=${2-1} # default exit status 1
  msg "$msg"
  exit "$code"
}

parse_params() {
  # default values of variables set from params
  flag=0
  param=''

  while :; do
    case "${1-}" in
    -h | --help)
      usage
      ;;
    -v | --verbose)
      set -x
      ;;
    --no-color)
      NO_COLOR=1
      ;;
    -f | --flag) # example flag
      flag=1
      ;;
    -p | --param) # example named parameter
      param="${2-}"
      shift
      ;;
    -?*)
      die "Unknown option: $1"
      ;;
    *)
      break
      ;;
    esac
    shift
  done

  args=("$@")

  # check required params and arguments
  [[ -z "${param-}" ]] && die "Missing required parameter: param"
  [[ ${#args[@]} -eq 0 ]] && die "Missing script arguments"

  return 0
}

parse_params "$@"
setup_colors

# script logic here

msg "${RED}Read parameters:${NOCOLOR}"
msg "- flag: ${flag}"
msg "- param: ${param}"
msg "- arguments: ${args[*]-}"

bashrc

Paste these function in the ~/.bashrc file.

Make a new folder and cd into it

  • Usage: mkcd name1
  • Code: mkcd(){ NAME=$1; mkdir -p "$NAME"; cd "$NAME"; }

Alias

  • Count files in directory: alias fcount='ls -1 | wc -l'
  • Disable "Save workspace" promt when closing R: alias R='R --no-save'
  • Tweak df: alias df='df -h'
  • Tweak du: alias du='du -h'

  • Using Exa instead of ls

    sh alias l='exa' alias la='exa -a' alias ll='exa -lah' alias ls='exa --color=auto'

More:

  • Finding out which linux you are using: uname -m && cat /etc/*release
  • Bulk renaming of files: rename 's/ch0/ch/gi' *.tiff

last 10 commands that ran in the current directory

Add this function to your .bashrc

``` sh title=".bashrc" function addhistory() { echo "{1%%'\n'}|${PWD} " >> ~/.history_ext }


Create file e.g. `folderhistory` with the content below and add it to your `$PATH`

``` sh title="folderhistory"
grep -v "folderhistory" ~/.history_ext | grep -a --color=never "${PWD}   " | cut -f1 -d"|" | tail

Source: https://github.com/natethinks/jog

System Information

Get system details

  • Get all environment variables: printenv
  • Get all configuration variables: getconf -a
  • Show ports/connections open: lsof
  • Get ubuntu version: lsb_release -r
  • Free disk space: df -h

System Performance Check

  • uptime
  • dmesg | tail
  • vmstat 1
  • mpstat -P ALL 1
  • pidstat 1
  • iostat -xz 1
  • free -m
  • sar -n DEV 1
  • sar -n TCP,ETCP 1
  • top

History

Press Ctrl+R to search through your history using auto-complete. Press Ctrl+R again and it will cycle though the other auto-completion options. Press Enter and the command will execute. Press ←,→ to edit commands.

  • Location of history file: echo $HISTFILE
  • Clear the history of current shell: history -c
  • Overwrite the history file with the current shell's history: history -c | history -w | exit
  • Delete first 15 entries: for i in {1..15}; do history -d 1; done
  • Clear history completly: ln -sf /dev/null ~/.bash_history && history -c && exit
  • Disable history: sudo echo "unset HISTFILE" >> /etc/profile
  • Disable history for user "0xfab1": echo "unset HISTFILE" >> /home/0xfab1/.bash_profile
  • Change number of lines stored in an ongoing history list session: echo "HISTFILESIZE=10 >> ~/.bashrc
  • Change amount of lines used for the history stack when it’s written to the history file: echo "HISTSIZE=0 >> ~/.bashrc
  • Top commands used: history | awk 'BEGIN {FS="[ \t]+|\\|"} {print $3}' | sort | uniq -c | sort -nr
  • Commands only used once: history | awk 'BEGIN {FS="[ \t]+|\\|"} {print $3}' | sort | uniq -c | sort -n | grep ' 1 '

More...

  • List open file descriptors (-i flag for network interfaces): lsof -i :8080
  • Stream current disk, network, CPU activity, etc: dstat -a
  • Trace system calls of a program: strace -f -e <syscall> <cmd>
  • Print currently active processes: ps1 aux | head -n20
  • Visualize process forks: ps1tree
  • Show size on disk for directories and their contents: du -ha
  • List currently open Internet/UNIX sockets and related informationnetstat | head -n20
  • Find hostname for a remote IP address: nslookup <IP address>
  • Current installed version: cat /etc/issue
  • Kernel information: uname -a
  • OS information: lsb_release -a
  • Device Information: lspci -v
  • Check the hostname of your machine: hostname
  • Shows last logged in users: last
  • Shows currently logged in user and groups for the user: id
  • List users on Linux: getent passwd
  • Show mounted drives: mount
  • Shows running kernel version: uname -ar
  • Show bash history, commands the user has entered previously: history

Disk Stuff

DD: low-level data dumping utility

  • burning an ISO image to USB stick is just one command away: sudo dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/sdb bs=1M
  • hard wipe a disk: sudo dd if=/dev/zero of=/dev/sda

DU: Disk usage command is used for quickly estimating the drive space used in a folder or partition

  • Show files and sort by size: /data/java$ du -sh * | sort -h

DF: Used for estimating disk space but for the entire disk rather than a directory or folder.

  • show which partition is how much full: df -h

MORE STUFF

  • Execute a command and report statistics about how long it took: time <cmd>
  • Send a process in current tty into background and back to foreground: CTRL + z ; bg; jobs; fg
  • Change Default Shell For A User: chsh -s /usr/bin/zsh username
  • Make and Change To That New Directory: mkdir new_dir && cd $
  • Configure Your Server Timezone: dpkg-reconfigure tzdata
  • Kill Everything Running On A Certain Portsudo kill "sudo lsof -t -i:3000"
  • See if the http status of the request changes: watch -d curl -LIs localhost:3000
  • Update access and modify time: touch README.md
  • Update access time: touch -a README.md
  • Update modify time: touch -m README.md
  • Show The Size Of Everything In A Directoryls | xargs du -sh
  • Saying Yes: yes | rm -r ~/some/dir
  • Show Disk Usage For The Current Directory: du -h | sort -nr

VIM

To make a default Vim installation more useful, type the following 5 lines into its .vimrc file:

set hls ic is nu noswf

Screen

Command Description
screen Create a new session.
Ctrl+A,D Detach from current screen session.
Ctrl+D End current session. Similart to exit.
screen -r Reattach to session.
screen -ls List all sessions.
screen -S <name> -L Create a new screen session <name> with logging enabled.
screen -r <name> Reattach to session with <name> if there are multiple ones.
screen -rx <name> Attach to session that is already attached.
Ctrl+A, Esc Enter scroll mode. Use ↑ and ↓ or Pg Up and Pg Dn to scroll. Hit Esc to exit scroll mode.

tmux

create a new tmux session

tmux

or create a new session with a name e.g. "SessionName"

tmux new-session -sSessionName

Use these commands to navigate between windows:

  • Control + B + N next session
  • Control + B + C new session

Join a tmux session (e.g. from a different device or user)

tmux attach

or be specific:

tmux attach-sesssion -t SessionName

Kill first window (0):

tmux kill-window -t 0

Kill a session:

tmux kill-session

Work with a file

  • Cat A File With Line Numbers: cat -n file
  • Line count in a file: wc -l <file>
  • Count unique words in a file: cat file.txt | xargs -n1 | sort | uniq -c
  • Display contents of a zipped text file: zcat <file.gz>
  • Copy a file from remote to local server, or vice versa: scp <user@remote_host> <local_path>
  • List Stats For A File: stat -x README.md
  • Securely Remove Filessrm -vz README.md or shred -uvz -n 5 README.md
  • Securely Remove Files after rm was used: sfill -lvz /home
  • Copying File Contents To System Paste Buffer: cat some-file.txt | pbcopy
  • Exclude A Directory With Find: find . -type f -not -path './.git/*' -ctime -10
  • File Type Info With File: file data.txt
  • Find Newer Files than this file: find blog -name '*.md' -newer blog/first-post.md
  • Get The Unix Timestamp: date +%s
  • Hexdump A Compiled File: cat Hello.class | hexdump -C
  • Grep For Files Without A Match: grep -L "foobar" ./*
  • Grep For Files With Multiple Matches: grep -rl "match1" src/css | xargs grep -l "match2"
  • Add "new entry" in line 13 of file "file.txt": sed -n -i 'p;13a new entry' file.txt
  • Remove lines under n (e.g. 6) characters: sed -E '/^.{,6}$/d' /path/to/input/file > /path/to/output/file or gsed -E '/^.{,6}$/d' /path/to/input/file > /path/to/output/file
  • Sort Alphabetically and Remove Duplicates: sort -us -o /path/to/output/file /path/to/input/file or bash -c "LC_ALL='C' gsort -us -o /path/to/output/file /path/to/input/file"

Validate

  • Valid IPv4 Address: grep -E -o "(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)"
  • Valid IPv4 CIDR Range: grep -E -o "^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])(\/(3[0-2]|[1-2][0-9]|[0-9]))"
  • Valid IPv6 Address: grep -E -o "^s*((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:)))(%.+)?s*"
  • Valid IPv4 CIDR Range: grep -E -o "^s*((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]d|1dd|[1-9]?d)(.(25[0-5]|2[0-4]d|1dd|[1-9]?d)){3}))|:)))(%.+)?s*(\/(12[0-8]|1[0-1][0-9]|[1-9][0-9]|[0-9]))"
  • Valid Hostname: grep -E -o "^(([a-zA-Z]|[a-zA-Z][a-zA-Z0-9-]*[a-zA-Z0-9])\.)*([A-Za-z]|[A-Za-z][A-Za-z0-9-]*[A-Za-z0-9])"
  • Regex Escape String: sed -E 's/([\.\\\+\*\?\[\^\]\$\(\)\{\}\=\!\<\>\|\:\-\#])/\\1/'

Network Stuff

  • Find Device in Monitoring Mode: iwconfig 2>/dev/null | grep "Mode\\:Monitor" | awk '{print $1}'
  • Find Access Point: iwconfig 2>&1 | sed -n -e 's/^.\*Access Point: //p'
  • Linux IPv6 search devices in local network: ping6 -c 2 -I en0 -w ff02::1
  • Show Linux network ports with process ID’s (PIDs): netstat -tulpn
  • Watch TCP, UDP open ports in real time with socket summary: watch ss -stplu
  • Show established connections: lsof -i
  • Change MAC address: macchanger -m MACADDR INTR
  • Change MAC address using ifconfig: ifconfig eth0 hw ether MACADDR
  • Get hostname for IP addressnbtstat -A x.x.x.x
  • Block access to e.g. "google.com" from the host machinetcpkill -9 host google.com
  • Enable IP forwarding: echo "1" > /proc/sys/net/ipv4/ip_forward
  • Change DNS to 1.1.1.1: echo "1.1.1.1" > /etc/resolv.conf
  • Nmap scan every interface that is assigned an IP: ifconfig -a | grep -Po '\b(?!255)(?:\d{1,3}\.){3}(?!255)\d{1,3}\b' | xargs nmap -A -p0-
  • Extract your external IP address using dig: dig +short myip.opendns.com @resolver1.opendns.com

DNS

Simple DNS performance check:

TIMEFORMAT=%R && (time dig @8.8.8.8 0xfab1.net) 2>&1 > /dev/null

Simple DNS performance check with loop through DNS list "dns.txt"

for dns in `cat dns.txt`; do echo -n $dns: && TIMEFORMAT=%R && (time dig @$dns 0xfab1.net) 2>&1 > /dev/null; done

dns.txt could look like this:

``` txt title="dns.txt" 1.1.1.1 8.8.8.8 9.9.9.9


Loop through DNS list and check website 10x

``` sh
TIMEFORMAT=%R && for dns in `cat dns.txt`; do (for i in {1..10}; do (echo -n $dns: && (time dig @$dns 0xfab1.net) 2>&1 > /dev/null); done); done

Fun Stuff

Entertaining nonsense:

  • Loop Train: for i in {1..10}; do sl; done

Alternatives for tree command:

-ls -R | grep ":$" | sed -e 's/:$//' -e 's/[^-][^\/]*\//──/g' -e 's/─/├/' -e '$s/├/└/' -find . -not -path '*/\.*' | python -c "import sys as s;s.a=[];[setattr(s,'a',list(filter(lambda p: c.startswith(p+'/'),s.a)))or (s.stdout.write(' '*len(s.a)+c[len(s.a[-1])+1 if s.a else 0:])or True) and s.a.append(c[:-1]) for c in s.stdin]"

If you don't have tree maybe create an as such: alias tree='command from above here'

Display all terminal colors

for x in {0..8}; do 
    for i in {30..37}; do 
        for a in {40..47}; do 
            echo -ne "\e[$x;$i;$a""m\\\e[$x;$i;$a""m\e[0;37;40m "
        done
        echo
    done
done
echo ""

Langton's ant simulation

echo -ne "\033#8";X=`tput cols`;Y=`tput lines`;((a=$X/2));((b=$Y/2));d=1;while case $d in 0)((a=a<2?X:a-1));;1)((b=b<2?Y:b-1));;2)((a=a==X?1:a+1));;3)((b=b==Y?1:b+1));; esac;do ((c=b+a*X));v=${k[c]:- };[ $v. = @. ]&&{((d=d>2?0:d+1));k[c]="";}||{(( d=d<1?3:d-1));k[c]=@;};echo -ne "\033[$b;${a}H$v";done

Other

  • Reboot: init 6
  • Compile C code: gcc -o output.c input.c
  • Compile 32 bit binary on 64 bit Linux: gcc -m32 -o output.c input.c
  • Disable bash history logging: unset HISTORYFILE
  • Connect to RDP server from Linux.rdesktop X.X.X.X
  • Kill current session: kill -9 $$
  • Clear bash history: cat /dev/null > ~/.bash_history
  • one-time table: for i in {1..12}; do for j in $(seq 1 $i); do echo -ne $i×$j=$((i*j))\\t;done; echo;done
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