variable
Assignment variable = 0, $ var access or $ {var}
$ N parameter
`` With live first performs primers (~ key)
Positional parameters
Environment Variables
/ etc / profile: global environment variables
. Bash_profile: the user's environment variables, in which the user's home, to take effect on which user
~ / .bashrc: the user's environment variables, in which the user's home, which will take effect on users
export: Export variables, meaning the user use outside
source: after modify environment variables allow variable file to take effect
Add a variable to the environment
Other variables can also export
Use environment variables in the script
Piping
| pipeline operator, serial command input and output, the output of a command passed to the next command
<Specified file as input, with basically nothing
> redirect the output, covering the original content
>> redirects output, does not cover the original content
& Background process
