Shell Script Series Tutorial Two: Start Shell programming

Shell Script Series Tutorial Two: Start Shell programming

2.1 How do I write a shell script?

(1) The most common use of VI or mcedit to write shell scripts, but you can also use any of your favorite editor;

(2) After the script is written, to set executable permissions for the script: syntax: chmod [option] Mode script-name

chmod +x script-name  chmod775 Script-name

here, 775 of these 3 numbers indicate this file for user (u), group (G), other user (o) permission settings, for example: the first 7, The binary is 111, which indicates that the user is given the read, write, and Execute permissions of this file respectively;

who: U (user), G (group), O (Other), a (user, default);  opcode: + (add permission),-(delete permission), = (reassign permission); Permission: R (Read permission), W (Write permission), X (Execute permission), s (set User ID number), t (Sticky bit)

1$chmodU+xfile# Add Execute permissions to the user of this file2$chmod 751# Give this file the user read and write execution permissions, the file group read, execute permissions, other users execute permissions3$chmodU=rwx,g=rx,o=xfile# and the previous statement mean the same4$chmod=rfile# Assign Read permissions to all users (the default user is a, this is the default)5$chmod 444 file# exactly the same as the previous statement6$chmodA-wx,a+rfile# The same as the previous clause,-represents removal Permissions7$chmod+r U+r Directory # recursively assigns read permissions to all files and subdirectories in the directory directory

(3) Use the following command to execute the script:

$ bash script-name or $ sh script-name or $./script-name (your terminal's current path is the path of the script, but you still need to add "./" To find the file from the current folder); (dot) indicates the execution of a given file within the current shell: The syntax is: . Command-name (see [2]).

Below, write down your first shell script: name it

$ clear $ echo " Hello World "

After you save the script, you might use the following command to execute the script:

$./first

This cannot be done because the script does not now have permission to execute: The screen will be emptied and Hello world will be printed on the screen.

chmod 775 first$.

Script commands	Meaning
Clear	Clear Screen
echo "Hello World"	Output the value of the information or variable on the screen, which makes the general use of the echo command: echo "Message"

Exercise : Write the following script, save and execute, observe the output

Ginfo

1 Clear2 Echo "Hello $USER"3 Echo "Today is \c";Date4 Echo "Number of User login: \c";W.H.O.|WC-L5 Echo "Calendar"6 Cal7Exit0

Output:

Hello Wangtoday is \c2016 Friday November 04Ten: $: theCstnumber of UserLogin: \c2Calendar November .Day 1234561  2  3  4  5   6  7  8  9 Ten  One  A   -  -  the  -  -  -  +   -  +  A  at  -  -  -   -  -  in  -    

2.2 Variables in the shell

In Linux (Shell), there are two types of variables:

1) System Variables : Custom and generated by Linux, all in uppercase letters.

2) User-defined variables (UDV): Variables defined and generated by the user.

Some important system variables are shown in the following table:

System variables	Meaning
Bash	Shell path: Like/bin/bash, this command is the same as the shell
Bash_version	Shell version, such as: 4.3.11 (1)-release
COLUMNS	The coloums of your terminal, such as 80; On my computer, when the terminal is maximized, this value becomes 205
HOME	The home path of the computer, such as/home/wang
LINES	and columns mean the same.
LOGNAME	Current user name, such as Wang
OSTYPE	OS type: such as Linux-gnu
PATH	Our path settings
PS1	Our prompt settings
Pwd	Current work Path
SHELL	Shell path: such as/bin/bash
Uesrname	Name of the user currently logged in to this PC

If you want to print out the current home path, you can:

echo $HOME      # output:/home/wang

But can you do that? The following command is OK without any errors, but it will output home instead of what the home refers to and add $ to the front of the home.

Echo Home    # Output: Home

2.3 Reading statement (read)

reading data from the keyboard is stored in the variable: syntax: Read var1, Var2, ..., Varn

Write the following script file, prompt the user to enter a name, the user uses the keyboard input name, stored in the specified variable, and then display:

VI Sayh Echo "  "read fname   # user input is stored inside the fname!!! Echo " Hello $fname, Lets be friend! "

Execute the following statement to run Sayh:

chmod +x sayh$. /sayh

Your First Name:
Zhao
Hello Zhao, Lets be friend!

2.4 Wildcard characters

Reference documents:

[1] Linux Shell Scripting tutorial:http://www.freeos.com/guides/lsst/index.html

[2] http://blog.csdn.net/mci2004/article/details/7182829

Shell Script Series Tutorial Two: Start Shell programming