1. What is the shell
Shell is a user interface to interact with the kernel, the most popular is called bash Shell Shell
Shell is a programming language <interpreted programming language>, that is a shell script
There may be more than a system shell, you can view the shell command system installed by cat / etc / shells, shell command syntax may support different is not the same
Implementation 2.Shell script
(1) The first: absolute or relative path input script first to be given permission to /root/helloWorld.sh ./helloWorld.sh + x
Alternatively, rather than giving + x permission, but with the interpreter interpreted sh helloworld.sh
(2) The second: bash or sh + script sh /root/helloWorld.sh sh helloWorld.sh
(3) The third: in front of the path of the script along with /root/helloWorld.sh ./helloWorld.sh "."..
Differences: first and second will open a new bash, bash the different variables can not be shared
3.Shell the variables
Linux Shell variables into the "system variables" and "user-defined variables", you can view the system variables set command
System variables: $ HOME, $ PWD, $ SHELL, $ USER, etc.
(1) displays all the current shell variables: set
(2) the definition of variables
Variable = value (e.g. STR = abc, A = 9)
No spaces on both sides of the equal sign
Variable names are generally accustomed to uppercase
Double and single quotes are different, only the double quotes space off Italy, single quotes will take off all special characters meaning