Get started with simple shell scripting

One, Shell script

Script: Can execute the file, after running can implement some function (command stack, non-interactive)

Standardize the general composition of shell scripts

#! Environmental Statement (Sha-bang)

# comment Text

Executable code

Second, simply write a shell script, according to international practice, or output Hello World

[Email protected] ~]# vim/root/1.sh

#!/bin/bash

echo Hello World

[Email protected] ~]# chmod +x/root/1.sh

[Email protected] ~]#/root/1.sh

Pipeline Delivery

Use | Pipeline operation

– The standard output from the previous command is given to the latter command to process

Third, redirect output

Collect only the correct output from the previous command

2>: Collect only the error output from the previous command

&>: Collect errors and correct output from the previous command

/dev/null #Linux黑洞设备, designed to collect not output results

Variables: In order to increase the ability of the script's applicable environment, increase the flexibility of the script, convenient.

Variables: containers, with immutable names, store changed values

Variable name = changed value

Use variable: $ variable name

To reduce the difficulty of using scripts, you can create interactive

READ: Can generate interaction to assign the contents of the keyboard input to a variable

What is a variable

Values that are stored as immutable names that may vary

– Variable name = variable Value

– Easy to reuse a value with a fixed name

– Improved adaptability to mission requirements and operational environment changes

Considerations when setting a variable

– If the specified variable name already exists, it is equivalent to re-assigning a value to this variable

– Don't have spaces on both sides of the equals sign

– Variable names are made up of letters/numbers/underscores, case-sensitive

– Variable names cannot start with a number, do not use keywords and special characters

Basic format

– Reference variable Value: $ variable Name

– View variable values: Echo $ variable name, echo ${variable name}

Types of variables

Positional variables

Command-line arguments (non-interactive pass-through values) that are provided when the script is executed

Pre-defined variables

The execution information used to save the script

– Use these variables directly

– You cannot assign values directly to these variables

$# The number of position variables that have been loaded

$* values for all positional variables

$? Status value after program exit, 0 indicates normal, other value is abnormal

$ (): The output of the command, as a parameter

Common Test Options

Check file status

-e: Document exists as true

-D: Document exists and is directory-True

-F: Document exists and is file-true

-r: Document exists with Read permission true

-W: Document exists with Write permission true

-X: Document exists with Execute permission true

Compare integer size (with E equals two words, g means greater than, L is less than)

-GT: Greater Than

-ge: greater than or equal to

-eq: Equals

-ne: Not equal to

-LT: Less than

-le: Less than or equal to

string alignment

= =: Equal

! =: Not Equal

For loop structure

Loop structure: The repeated execution of the statement, loop to execute

For variable name in value list

Do

Command sequence

Done

Get started with simple shell scripting