linux

• IPtables

• Netplan

• Bash

  • Ejemplo bucle For
  • Ejemplo bucle While infinito

• Shell-script

  • Inicio Bash
  • Function
  • IF - ELIF - ELSE - FI
  • Petición parámetros
  • case

• Diff

---

IPtables

sudo apt-get install iptables-persistent netfilter-persistent

vi  /etc/iptables/rules.v4 
# Generated by iptables-save v1.6.1 on Thu Mar  5 11:22:52 2020
*filter
:INPUT DROP [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:LOGGING - [0:0]
-A INPUT -i lo -j ACCEPT
-A INPUT -d 127.0.0.0/8 ! -i lo -j REJECT --reject-with icmp-port-unreachable
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -s 192.168.14.0/25 -p tcp -m tcp --dport 22 -m comment --comment "SSH" -j ACCEPT
-A INPUT -p icmp -m comment --comment "PING" -j ACCEPT
-A INPUT -j LOGGING
-A LOGGING -m limit --limit 2 \/min -j LOG --log-prefix "IPTables:DROP: "
-A LOGGING -j DROP
COMMIT
\# Completed on Thu Mar  5 11:22:52 2020 \

 
vi /etc/rsyslog.d/40-iptables.conf
:msg, regex, "iptables:" -/var/log/firewall.log
& ~

sudo /etc/init.d/rsyslog restart

Netplan

Ejemplo fichero netplan:

vi /etc/netplan/99-netcfg.yaml 
network:
   version: 2
   renderer: networkd
   ethernets:
     ens192:
       dhcp4: no
       dhcp6: no
       addresses:
         - 192.168.1.100/24
       gateway4: 192.168.1.1
       nameservers:
         addresses:
           - 9.9.9.9
           - 8.8.8.8 
      
netplan apply

---

Bash

Ejemplo Bucle For

for i in $(ls -a); do echo "fichero ${i}"; done

Ejemplo Bucle While infinito

while [ true ]; do echo "hello world\n"; sleep 3; done

---

Shell-script

Inicio bash

#!/bin/bash

ECHO=$(which echo)
CAT=$(which cat)
NMAP=$(which nmap)
RM=$(which rm)
DIFF=$(which diff)
 ...

Function

function Usage () {
        ${ECHO} -e "SYNTAX ERROR: ${0} [opcion1|opcion2] <nombre>\n"
        exit 1
}

IF - ELIF - ELSE - FI

Verificamos los parametros si son nulos, y si primer parametro contiene valor correcto.

if [[ -z ${1} ]] || [[ -z ${2} ]] ; then
  Usage
elif [[ "${1}" != "opcion1" ]] && [[ "${1}" != "opcion2" ]] ; then
  Usage
else
	accion="${1}"
	nombre="${2}"
fi

Si fichero existe entonces lo borramos:

if [[ -f "${nombreFichero}" ]] ; then
  ${RM} ${nombreFichero}
fi

Petición parámetros

${ECHO} "Introduce un nombre:"
read -s nombre

Case

case $opcion in
  0)
    ${ECHO} -e "[CORRECTO];"
    ;;
  *)
    ${ECHO} -e "[INCORRECTO];"
    ;;
esac

---

Diff

Ejemplo visualización en columnas

diff -y fichero1.txt fichero2.txt

Ejemplo comparar sin diferenciar espacios en blanco ni tabuladores

diff -wEZB  fichero1.txt fichero2.txt

Ejemplo modo silencioso

Importa el resultado del commando diff result=0 EXIT OK, result=1 FAIL.

result=$(diff -q --ignore-matching-lines="ntp clock-period" fichero1.txt fichero2.txt)

Ejemplo ignorando lineas

Las líneas con contenido "ntp clock-period" son ignoradas.

diff --ignore-matching-lines="ntp clock-period" fichero1.txt fichero2.txt

Comandos utilies del diff

diff 
      --suppress-blank-empty     suppress space or tab before empty output lines
      -y, --side-by-side         output in two columns
      -w, --ignore-all-space     ignore all white space
      -B, --ignore-blank-lines   ignore changes where lines are all blank
      -i, --ignore-case          ignore case differences in file contents
      -E, --ignore-tab-expansion ignore changes due to tab expansion
      -q, --brief                report only when files differ
      --suppress-common-lines    do not output common lines

---

URLs Referencia:

• https://www.computerhope.com/unix/udiff.htm