Bash

User -> Terminal -> Bash -> Kernel -> System Resources

ls /tmp
echo $?

echo $SHELL
ps -p $$

bash --version

type cd
type ls
which ls
command -v python3

command [options] [arguments]

ls -lah /var/log

pwd

cd /etc
cd ..
cd ~
cd -

ls
ls -l
ls -la
ls -lah

touch file.txt
mkdir notes
mkdir -p project/{src,docs,tmp}
cp file.txt backup.txt
cp -r dir1 dir2
mv old.txt new.txt
rm file.txt
rm -r folder
rm -rf folder

cat file.txt
less file.txt
head -n 20 file.txt
tail -n 20 file.txt
tail -f app.log
nl -ba file.txt

find /var/log -name "*.log"
find . -type f
find . -type d
find . -type f -size +10M
find . -type f -mtime -1

keyboard -> stdin
stdout   -> normal output
stderr   -> errors

command > out.txt
command >> out.txt
command 2> err.txt
command > out.txt 2> err.txt
command &> all.txt
command > /dev/null 2>&1

sort < names.txt

cat <<EOF
line 1
line 2
EOF

cat <<'EOF'
$HOME will not expand here
EOF

grep root <<< "root:x:0:0"

cat access.log | grep 404 | wc -l

grep 404 access.log | wc -l

grep "error" app.log
grep -i "failed" auth.log
grep -r "password" .
cut -d: -f1 /etc/passwd
sort users.txt
sort -u users.txt
uniq names.txt
uniq -c names.txt
wc -l file.txt
tr 'a-z' 'A-Z' < file.txt
sed 's/http/https/g' urls.txt
awk '{print $1}' file.txt
column -t data.txt

ss -ltn | tail -n +2 | wc -l
cut -d: -f1 /etc/passwd
grep -i "failed password" auth.log | awk '{print $(NF-3)}' | sort -u

cat hosts.txt | xargs -I{} ping -c 1 {}
find . -name "*.log" | xargs rm
find . -type f -print0 | xargs -0 sha256sum

name="zoro"
port=4444
path=/tmp

echo "$name"
echo "$port"

export TARGET=10.10.10.10
export WORDLIST=/usr/share/wordlists/rockyou.txt
printenv
env

echo "$HOME"
echo "$USER"
echo "$PATH"
echo "$PWD"
echo "$OLDPWD"
echo "$?"
echo "$$"

read name
echo "Hello $name"
read -p "Target IP: " ip
read -s -p "Password: " pass; echo

echo '$HOME'

echo "$HOME"
echo "User: $USER"

file="my notes.txt"
cat $file

cat "$file"

now=$(date)
user_count=$(cut -d: -f1 /etc/passwd | wc -l)

x=5
y=7
echo $((x + y))

echo file{1..5}.txt
mkdir -p lab/{loot,scans,notes}

ls *.txt
ls /var/log/*.log

cd ~
cat ~/.bashrc

if [ -f /etc/passwd ]; then
  echo "file exists"
fi

if [ "$USER" = "root" ]; then
  echo "running as root"
else
  echo "not root"
fi

[ condition ]
[[ condition ]]
test condition

[ -e file ]
[ -f file ]
[ -d dir ]
[ -r file ]
[ -w file ]
[ -x file ]
[ -s file ]

[[ -z "$var" ]]
[[ -n "$var" ]]
[[ "$a" = "$b" ]]
[[ "$a" != "$b" ]]

[ "$x" -eq 10 ]
[ "$x" -ne 10 ]
[ "$x" -lt 10 ]
[ "$x" -le 10 ]
[ "$x" -gt 10 ]
[ "$x" -ge 10 ]

if [[ -f file && -r file ]]; then
  cat file
fi

if [[ "$port" -eq 80 || "$port" -eq 443 ]]; then
  echo "web port"
fi

case "$1" in
  start) echo "starting" ;;
  stop) echo "stopping" ;;
  restart) echo "restarting" ;;
  *) echo "usage: $0 {start|stop|restart}" ;;
esac

for host in 10.10.10.1 10.10.10.2 10.10.10.3; do
  ping -c 1 "$host"
done

count=1
while [ "$count" -le 5 ]; do
  echo "$count"
  count=$((count + 1))
done

while IFS= read -r line; do
  echo "$line"
done < hosts.txt

until ping -c 1 10.10.10.10 >/dev/null 2>&1; do
  sleep 1
done

for i in {1..10}; do
  [ "$i" -eq 5 ] && continue
  [ "$i" -eq 9 ] && break
  echo "$i"
done

say_hello() {
  echo "hello"
}

say_hello

scan_host() {
  local host="$1"
  nmap -Pn "$host"
}

scan_host 10.10.10.10

is_root() {
  [ "$EUID" -eq 0 ]
}

if is_root; then
  echo "yes"
fi

get_date() {
  date +%F
}

today=$(get_date)

foo() {
  local tmp="value"
  echo "$tmp"
}

hosts=(10.10.10.10 10.10.10.20 10.10.10.30)
echo "${hosts[0]}"
echo "${hosts[@]}"
echo "${#hosts[@]}"

for host in "${hosts[@]}"; do
  echo "$host"
done

msg="bash scripting"
echo "${#msg}"

echo "${msg:0:4}"

file="report.txt"
echo "${file/.txt/.md}"

echo "${name:-guest}"
: "${port:=8080}"

sleep 100
sleep 100 &

jobs
fg %1
bg %1
kill %1

ps aux
ps -ef
pgrep ssh
pidof bash

kill 1234
kill -9 1234
pkill firefox
killall nc

nohup long_task.sh > task.log 2>&1 &
disown

-rwxr-x---

chmod 644 file.txt
chmod 755 script.sh
chmod +x script.sh
chmod -R 750 project

chown user file.txt
chown user:group file.txt
chown -R user:group project
chgrp developers script.sh

umask
umask 022

ping -c 1 8.8.8.8
curl -I https://example.com
wget -qO- https://example.com

ss -lnt
ss -lun
netstat -tulnp
lsof -i :80

exec 3<>/dev/tcp/example.com/80
echo -e "GET / HTTP/1.1\r\nHost: example.com\r\nConnection: close\r\n\r\n" >&3
cat <&3

for port in 22 80 443 445 8080; do
  timeout 1 bash -c "echo >/dev/tcp/10.10.10.10/$port" 2>/dev/null && echo "Port $port open" || echo "Port $port closed"
done

curl -O http://server/file
wget http://server/file -O tool.sh
chmod +x tool.sh
./tool.sh

#!/usr/bin/env bash

#!/usr/bin/env bash

echo "Hello, Bash"

chmod +x hello.sh
./hello.sh

#!/usr/bin/env bash

echo "Script: $0"
echo "Arg1: $1"
echo "Arg2: $2"
echo "Count: $#"

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

main() {
  echo "Safe Bash template"
}

main "$@"

#!/usr/bin/env bash
set -euo pipefail

while IFS= read -r host; do
  if ping -c 1 -W 1 "$host" >/dev/null 2>&1; then
    echo "[+] $host is up"
  else
    echo "[-] $host is down"
  fi
done < hosts.txt

#!/usr/bin/env bash
set -euo pipefail

target="${1:-}"
[ -z "$target" ] && { echo "Usage: $0 <target>"; exit 1; }

mkdir -p recon
host "$target" | tee recon/dns.txt
whois "$target" | tee recon/whois.txt

bash -x script.sh

set -x
set +x

bash -n script.sh

shellcheck script.sh

rm -rf $dir
rm -rf -- "$dir"

for line in $(cat file.txt); do
  echo "$line"
done

while IFS= read -r line; do
  echo "$line"
done < file.txt

find . -type f | wc -l
find . -maxdepth 1 -type d
du -sh *
ls -lahS

cut -d: -f1 /etc/passwd
id
uname -a
hostnamectl

grep -i error /var/log/syslog | tail -n 20
journalctl -xe
journalctl -u ssh

ip a
ip r
ss -tulpn
arp -a

sha256sum file
md5sum file
base64 file
base64 -d encoded.txt

for ip in $(seq 1 10); do
  ping -c 1 192.168.1.$ip >/dev/null && echo "192.168.1.$ip up"
done

name="value"
echo "$name"
if [[ -f file ]]; then echo yes; fi
for x in a b c; do echo "$x"; done
while IFS= read -r line; do echo "$line"; done < file.txt
f(){ local x="$1"; echo "$x"; }
set -euo pipefail
IFS=$'\n\t'

>      stdout overwrite
>>     stdout append
2>     stderr overwrite
2>>    stderr append
<      stdin from file
<<     heredoc
<<<    herestring
|      pipe stdout to stdin

[[ -f file ]]
[[ -d dir ]]
[[ -z "$x" ]]
[[ -n "$x" ]]
[[ "$a" == "$b" ]]
[[ "$n" -gt 10 ]]

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

main() {
  :
}

main "$@"