Basics of Linux Shell scripting here we first talk about the shell of the basic syntax, the beginning, comments, variables and environment variables, to do a basic introduction, although not related to specific things, but lay the foundation is to learn easily after the premise.
1. Linux Scripting Basics
Basic Introduction to 1.1 grammar
1.1.1 Opening
The program must start with the following line (must be in the first line of the file):
#!/bin/sh
The symbol #! is used to tell the system that the parameter behind it is the program used to execute the file. In this example we use/BIN/SH to execute the program.
When you edit a script, you must also make it executable if you want to execute the script.
To make the script executable:
Compile chmod +x filename so you can use./filename to run
1.1.2 Notes
In shell programming, a sentence that begins with # represents a comment until the end of the line. We sincerely recommend that you use annotations in your programs.
If you use annotations, you can understand the script's function and how it works in a very short time, even if you haven't used the script for quite a long period of time.
1.1.3 Variable
In other programming languages, you must use variables. In shell programming, all variables are made up of strings, and you do not need to declare the variables. To assign a value to a variable, you can write:
#!/bin/sh
#对变量赋值:
A= "Hello World"
# now print the contents of variable a:
echo "A is:"
Echo $a
Sometimes variable names are easily confused with other words, such as:
num=2
echo "The $numnd"
This does not print out "This is the 2nd" and simply prints "This is the" because the shell will go to search for the value of the variable numnd, but this variable has no value. You can use curly braces to tell the shell that we're printing num variables:
num=2
echo "This is the ${num}nd"
This will print: This is the 2nd
1.1.4 Environment variables
Variables processed by the EXPORT keyword are called environment variables. We do not discuss environment variables, because environment variables are typically used only in logon scripts.
This is explained here, and below we will be exposed to the substantive parts of the specific Linux Shell Script Foundation.
The above is the detailed introduction of the Linux shell Script Basic Learning (a), more relevant content please pay attention to topic.alibabacloud.com (www.php.cn)!
