Linux operational ENGINEER1.4 (Shell Scripting Basics)

ENGINEER1.4

Shell Script Basics

Understanding the shell environment

How bash shells are used

Interactive:

--manual intervention, high degree of intelligence

----explain execution by article, low efficiency

Non-interactive:

-Need to design in advance, the difficulty of intelligence is big;

--Batch execution, high efficiency;

-Easy to implement in the background and quietly;

What is Shell scripting : Designing executable statements in advance to complete a specific task's files

--Explanatory program

--Sequential, batch execution

Standardize the general composition of shell scripts:

#！ Environmental statement

#注释文本

Executable code

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Example 1:

Writing the helloworld.sh greeting script

1. Write script code:

   #vim/root/helloworld.sh

   #！ /bin/bash

   echo "Hello World"

2. Add x Execute Permissions

   #chmod +x/root/helloworld.sh

3. Run a script test

   #/root/helloworld.sh

Example 2:

Writing System Information Report scripts

1. Write script code:
   

   #vim/root/1.sh

#!/bin/bash

Cat/etc/redhat-release

Uname-r

Hostname

2. Add x Execute Permissions

# chmod +x/root/1.sh

3. run the script test:

#/root/1.sh

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Simple Scripting Tips

Application of redirected output

: Collect only the correct 2>: Collect only error &>: Collect all

This example requires writing a script/root/out.sh with the following features:

1. Execute this script to show I Love study!!

2. The execution/root/out.sh 2> Err.log should not be displayed, but the contents of the view Err.log file are I Love study!!

Steps:

1. #vim/root/out.sh
   

   #!/bin/bash

   #echo "I love study!!" >&2

2. #chmod-X/root/out.sh

3. #/root/out.sh

4. #/root/out.sh 2>err.log

5. #cat Err.log

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Definition and use of variables

Store a value that may change with an immutable name

Reference variable Value: $ variable name with {} to define easily confusing names

Types of variables:

vary depending on the purpose of the variable:

Environment variables: variable names are generally capitalized to set the user, System environment (PATH)

positional variables:bash built-in, command-line arguments provided when storing built-in scripts $n, n is ordinal $ ... ${10}

Predefined variables:bash built-in, special values that can be called directly, cannot be modified directly

$#: Number of position variables loaded $*: The value of all positional variables $?: state value after exit of program, 0 indicates normal, other exception

Custom variables: user-owned design, modification and use

Cases:

Requires writing a script/root/myhead with the following features:

This script can receive 2 positional parameters and can be executed in the following format

After this script executes, you can display "you have provided a total of $# parameters," and then the next line shows "the file's top $:", immediately following the next line to start outputting the first few lines of the corresponding file

Step one : write/root/myuseradd to add a user's script

#vim/root/myuseradd

#！ /bin/bash

echo "provides a total of $ #个参数"

echo "Username is $ $, password is $"

Useradd $

echo "$" | passwd--stdin $

Two. Add Execute Permissions

#chmod-X/root/myuseradd.sh

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Common Test options:

• File status detection-F,-D,-E,-R,-W,-X

• Integer values compare-gt,-ge,-eq,-ne,-lt,-le

• string comparison = =,! =

• Take the counter action!

Multi-Branch If selection structure:

If condition test action 1 then command sequence 1

elif condition Test Action 2 then command sequence 2

else Command Sequence 3

Fi

Cases:

This example requires the creation of a/root/foo.sh script on the virtual machine Server0, with the following objectives:

1. When running/root/foo.sh Redhat, the output is Fedora

2. When running/root/foo.sh fedora, the output is Redhat

3. When no parameters or parameters are not redhat or fedora, the error output produces the following information:/root/foo.sh Redhat|fedora

1) Writing script code

[Email protected] ~]# vim/root/foo.sh
#!/bin/bash
If ["$" = "Redhat"]
Then
echo "Fedora"
elif ["$" = "Fedora"]
Then
echo "Redhat"
Else
echo "/root/foo.sh Redhat|fedora" >&2
Fi

2) Add x Execute Permissions

[Email protected] ~]# chmod +x/root/foo.sh

Step two: Test foo.sh judgment Script

1) test conditions that provide the correct parameters

[Email protected] ~]#/root/foo.sh redhat Fedora
[Email protected] ~]#/root/foo.sh Fedora Redhat

2) test to provide unexpected parameters

[Email protected] ~]#/root/foo.sh Ubuntu
/root/foo.sh Redhat|fedora

3) test conditions that do not provide parameters

[Email protected] ~]#/root/foo.sh
/root/foo.sh Redhat|fedora

This article is from the Linux OPS blog, so be sure to keep this source http://13401400.blog.51cto.com/13391400/1979741

Linux operational ENGINEER1.4 (Shell Scripting Basics)