Bash Learning ahead

#!/bin/sh

#!/bin/bash

View Shell version

Bash--version

Bash vulnerability

The Bash vulnerability is a vulnerability in software that controls the command prompt for a Linux computer. exploiting this vulnerability, an attacker could take over the entire operating system of a computer, access confidential information, make changes to the system, and so on. Anyone's computer system, if you use bash software, you need to patch it up immediately.

This burst of bash vulnerability is that bash handles such "function environment variables" and does not end with the function End "}", but executes the subsequent shell commands! For example

Envx= ' () {:;}; Echovulnerable ' Bash-c "Echothisisatest"

If you return
Vulnerable
This is a test
If such a result, please upgrade as soon as possible

echo $USER (System variable)

Defining global Variables in/etc/profile

source/path/file.sh =. /path/file.sh is different from sh

You can bring the variables in the current script to the current shell

Vim a.sh

#!/bin/sh

Source/etc/init.d/functions

Action "It is a test Deamon"/bin/true

Troubleshooting commands

Dmesg

Cat/var/log/message

Script Cleanup/var/log/messages

#!/bin/sh

User=0

dir=/var/log/

If ["$USER"-ne "$UID"]then

echo "You must root"

Exit 1

Fi

CD $DIR

Cat/dev/null >messages && echo "It is clear"

Exit 0

Bash Learning ahead