The user environment is defined by various variables (environment variables, shell variables). Environment variables are variables that are valid for the shell itself or for all processes launched from it. A shell variable is that shell. Only valid within. You can change shell variables to environment variables by exporting them with the *** export *** command, and with the *** env *** and *** printenv *** commands. You can display environment variables, shell variables and environment variables with the *** set *** command.
Shell options
Syntax: *** set [-o] [+ o] [option] *** Specify -o to enable option, + o to disable option
Alias
You can use the alias function (*** aliias *** command) to give an alias to a command, or to treat commands and options as a group like a new command. Use the *** unalias *** command.
Example) alias ls ='ls -l' However, even if you are using the alias function, you can execute it without options by typing *** \ ls *** etc.
Function definition
You can use the *** function *** command to define your own functions available on the bash shell.
Syntax: *** [function] {function name} () {command} *** function can be omitted. Half-width space is required in {}.
Use the *** declare -f *** command to display the defined function and the *** unset *** command to delete it.
bash config file
To set environment variables, aliases, and functions automatically when the shell is started, describe them in the configuration file.
-[] / etc / profile ... Executed at login. -[] /etc/bash.bashrc ... Executed when bash starts.
A shell script is a text file with commands written in it. The execution method is *** bash {script file name} ***, *** source {script file name} , ". **" * "," *** chmod a + x {script file name} *** ".
File check
Syntax: test {conditional statement} Conditional statement: Returns 0 if true, non-zero if false. -f {file} ... True if there is a file -d {directory} ... True if there is a directory Numerical value 1 -eq Numerical value 2 ... True if numerical value 1 and numerical value 2 are equal Character string 1 = Character string 2 ... True if character string 1 and character string 2 are equal
Control structure
Syntax 1: if conditional expression then Execution statement 1 else Execution statement 2 fi
Syntax 2: case expression in Value 1) Execution statement 1 ;; Value 1) Execution statement 1 ;; esac
Syntax 3: for variable name in list of values to assign to the variable do Execution statement done
Syntax 4: while conditional statement do Execution statement done
Shell script execution environment
To execute it, write *** #! / Bin / bash *** at the beginning of the script.