Shell Script (vii)

Shell Script (vii)

J, Array

#关联数组: A generic array index must be a numeric value, and an associative array index can be a string

#也可以是数值, similar to a Python dictionary

awk ' BEGIN {str[name]= ' string '; str[1]= "1"};p rintf ("%s\n%s\n", str[name],str[1])}650; "this.width=650"/HTTP// S3.51cto.com/wyfs02/m01/6e/43/wkiol1v35uehnj1waaa90val3ge089.jpg "/>

#split函数, note that the for (I-in name) output is random

Awk-f: ' {split ($0,name, ': '); for (I-in name) print I, ":", Name[i]} ' num.txt

Awk-f: ' {split ($0,name, ":"); for (i=1;i<=nf;i++) print I, ":", Name[i]} ' num.txt

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M01/6E/47/wKiom1V346KyAbQbAADQmw2eHtQ792.jpg "/>

#数组形式的系统变量, Enviro storage is a system environment variable

awk ' BEGIN {for (i in ENVIRON) print i "=" environ[i]} '

5. Variables and references

(1) Variables

A, variable substitution and assignment

Symbols such as #变量名只能包含大小写字母, numbers, draw lines, etc., and cannot start with a number

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/6E/43/wKioL1V35Uiyd0FfAAEMiYRXdlg310.jpg "/>

#变量赋值

Var=value: Assigning value values to Var

Var+value: Reset the value of the assigned Var

Var?value or Var:?value: Displays system error messages for unassigned Var

Var:=value: Assigns value to an unassigned Var

Var:-value: Assigns value to an unassigned Var, but value does not store the address space corresponding to Var

Echo ${name:-carl}

Echo ${name:=carl}

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/6E/47/wKiom1V346OCcG1tAACOhVZopG4175.jpg "/>

Echo ${var?test}

Echo ${var:?test}

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M00/6E/43/wKioL1V35UjQLczjAABn9thR5e0014.jpg "/>

#设置只读变量

ReadOnly rdonly

B, untyped shell script variables

#shell的变量是无类型的, floating-point type not supported, only shaping and character type supported

#字符型变量有一个默认整型值0, the character variable is empty by default, and the string is assigned to the integer type directly

#变量, the integer variable becomes a character variable, and the character variable is increased by 1, and the variable becomes

#整型, and the value is 0

Name= "Test"

Num= "123"

#将字符变量name强制转换成整型, the value is also "test"

#转换后直接当数值使用, the default value is =0

Declare-i Name

Echo $name

#将字符型变量自增1, it becomes an integral type. If the variable value is all numbers, it is used as an integral type

Let name++

Echo $name

Let name++

Echo $name

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M00/6E/47/wKiom1V346OQwXNQAADCHxDlHNY486.jpg "/>

c, Environment variables

#定义和清除环境变量, environment variables generally use uppercase letters

Myls=/bin/ls

Export Myls

Echo $MYLS

$MYLS

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M01/6E/43/wKioL1V35UmQcktfAAC8cXBLb_4813.jpg "/>

#清除环境变量, the value of the variable becomes empty by default

unset Myls

Echo $MYLS

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M01/6E/47/wKiom1V346Syd_aSAAA2c5Dm-uk988.jpg "/>

#常用环境变量

PWD: Current Working directory

OLDPWD: Last working directory

Path: Indicates the path to the executable file

HOME: The root directory of the current user

SHELL: Default is/bin/bash

User: Login username

UID: Login User ID

PPID: Creates the process number of the current process, which is the parent process number of the current process

PS1: Prompt variable to set the first-level shell prompt format, default to "[\[email protected]\h \w]\$"

PS2: Prompt variable, used to set level two shell prompt format, default to ">", enter the incomplete command will be displayed

\u: Indicates the current user name

\@: Indicates time is displayed in 12-hour system

\h: Indicates host name

\w: Indicates the current working directory name

\w: Represents the full name of the current working directory

\$: If the UID is 0, print "#"; otherwise, print "$"

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/6E/43/wKioL1V35UnwPNSRAADPy1WZ_wE319.jpg "/>

#IFS: Shell field delimiter, default to space, to ":", space separated by field from field

Export ifs=:

Echo $PATH

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/6E/47/wKiom1V346Tg_8uTAABN40ZxlSQ536.jpg "/>

#环境变量配置文件:. Bash_profile,. BASHRC,. Bash_profile and/etc/profile

#前3个全部以隐藏形式存放到 $HOME/down, for the corresponding user, and finally for the global settings

d, Position parameters

(2) References

A, full reference and partial references

B, Command substitution

C, Escape

6. Exit, test, judgment and operator

(1)

7. Advanced usage of Variables

8. I/O redirection

9. Child shell and process processing

10. Functions

11. Aliases, lists, and arrays

12. Script Debugging

13. Shell Combat

This article is from the "Love On Action" blog, please be sure to keep this source http://1055745601.blog.51cto.com/5003160/1660425

Shell Script (vii)