Shulou(Shulou.com)06/03 Report--

Shell Script Concept

1. Save the commands to be executed in sequence to a text file

2. Give the file executable permission and it can run.

3, can be combined with a variety of shell control statements to complete more complex operations

Shell Script Application Scenario

1. Repeatable operation

2. Batch transaction processing

3. Automated operation and maintenance

4. Monitoring of service operation status

5. Timing task execution

Perfect shell script composition

1. Script declaration

2. Executable statements

3. Comment text

Shell's Role--Command Interpreter,"Translator"

Execution script file method complete

Method 1: Script file path (absolute and relative)

Method 2: sh script file path

Method 3: Source Script File Path

Method 4:

[root@localhost ~]#. first.sh

Summary:

1. Except.../ First.sh needs to be assigned execution permission before it can be executed, and the rest of the execution file commands do not need to be assigned and can be executed directly;

2.sh.first.sh vs./ First.sh does not change the current directory location after executing the file

interactive hardware device

Standard Input: Data received from the device as input by the user

Standard Output: Output data to the user through the device

Standard Error: An execution error message is reported by this device

1. Redirect operations

2. Pipeline operation symbol "|"

Output the result of the command on the left as the target of the command on the right

awk: vertical recognition

The command in the figure can be converted:

awk -F: '{print $1,$7}'=awk -F":" What the variable '{print $1,$7}' does

1. Provide specific parameters for flexible management of Linux systems, with two layers of meaning.

Variable Name: Use a fixed name, preset by the system or defined by the user

Variable value: can change according to user settings and system environment changes

the type of a variable

1. Custom variables: defined, modified and used by users themselves

2. Environmental variables: maintained by the system and used to set the working environment

3. Position variable: pass parameters to script program through command line

4. Predefined variables: a class of variables built in Bash that cannot be modified directly

Define a new variable

Variable names start with a letter or underscore, case sensitive, all caps recommended

View variable names

Use quotation marks when assigning

Single quotes: Prohibited from quoting other variable values,$is treated as an ordinary character

Double quotes: Allow references to other variable values via the $sign

Reverse apostrophe: command replacement, extract the output of the command after execution

Input from keyboard assigns variable values

Set the scope of a variable

The two formats can be mixed

Operations on integer variables

Common operators

Addition: +

Subtraction: -

Multiplication: \ *

Division: /

Modulus (remainder): %

environment variable

1. Created by the system in advance to set the user's working environment

Configuration files: /etc/profile,~/.bash_profile

2. Environment variables created

PWD、PATH

USER、HOME、SHELL

position variable

1, expressed as $n, n is a number between 1 and 9

[root@localhost ~]# ./ myprog.sh one two three four five six

./ myprog.sh:$0(name of currently executing process)

one:$1 (1st position parameter)

two:$2 (2nd position parameter)

six:$6 (6th position parameter)

predefined variables

●$#: Number of positional variables in the command line

●$*: Contents of all position variables

●$?：The status returned after the execution of the previous command. When the returned status value is 0, it indicates execution.

Line normal, non-zero value indicates execution exception or error

●$0: Name of currently executing process/program

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