Rules for defining variable names:
Variable names are strictly case-sensitive, can't have special characters, start with a number, and can't have any spaces on both sides of the equal sign. Learn as much as possible about the meaning of variable names.
1, basic mode
Assign directly to a variable, variable name = variable value.
2. Assign the command execution result to the variable
3. Define variables interactively (read)
Objective: It is more flexible for users to assign values to variables themselves.
Explanation of common options:
-p defines the information to prompt the user.
-n defines the number of characters (limits the length of variable values)
Do not display -s (do not display user input)
-t defines the timeout, and the default unit is seconds (which limits the timeout for users to enter variable values).
4. Define typed variables (declarations)
Objective: to make some restrictions on variables and fix the types of variables, such as integer and read-only.
Usage: declare option variable name = variable value
Common options:
-I declare the variable as an integer. -i A= 123.
-r defines the read-only variable declare -r B=hello.
Unset variable name
Similarity: the contents in quotation marks can be taken as a whole.
Difference: Double quotation marks can refer to variables, while single quotation marks cannot refer to variables.
*: Matches 0 or any number of characters.
? : Any single character
[a-z]: Any single character in parentheses.
! Take the opposite approach
{string, string, string}: Matches all strings separated by commas in brackets.
{1 ... 100}: Match a sequence.
Case:
1. Script name * * *. hush
2. Script content
1) defines the parser.
#! /bin/bash
#! /bin/env bash Advantages: It will automatically find the parser location of the current system.
2) Precautions
#
3) the program itself
Define variables+basic commands+basic grammar+ideas
1. Standard script execution method: relative path or absolute path.
Prerequisite: The standard execution mode script must have executable permissions.
2. Non-standard implementation method (not recommended)
Scenario: View the script execution process; Or the script cannot provide executable permissions.
Parser+script file