variable:
The rules define the variables:
1) Variable names can consist of letters, digits, and underscores, but can not start with a number
2) on both sides of the equal sign can not have spaces
3) general custom variable name in uppercase
The return value of the command assigned to a variable:
1) using the command `` quotes
2) using the $ () to perform
Set the environment variable:
The basic syntax:
1) export variable name = variable value output is not the shell variable environment variables
2) source profile allows configuration information after the changes take effect immediately
3) echo $ variable name query environment variables
Multiline comments:
Location parameter variables:
When we execute a shell script, if you want to get to the command line parameters, you can use the position parameter variables. As ./myshell.sh 100 200, which is a command-line shell execute, you can get the parameter information myshell script.
The basic syntax:
$ N: n is a number, $ 0 for the command itself, $ 1- $ 9 representing the first to ninth parameter, it needs to contain more than ten parameters {10} $ braces
$ *: On behalf of all the command line parameters
$ @: On behalf of all the command line parameters, but each parameter will be treated separately
$ #: The number of all parameters
Predefined variables:
shell designers have designed a pre-defined variables that can be used directly in a shell script.
PID of the current process: 1) $$
2) $ !: The last process running in the background process ID
3) return to the state $ ?: command last executed. If this variable is 0, demonstrated the correct execution of a command; if the variable is non-zero, then the proof is not correct on a command
