Shell script Introduction, script structure and execution, date command usage, variables in scripts

20.1 Shell Script Introduction

What is a shell?

• Shell is a scripting language
• You can use logical judgments, loops, and other syntax
• Functions can be custom-defined
• The shell is a collection of system commands
• Shell scripts enable automated operations, which can greatly increase our operational efficiency

20.2 shell script Structure and execution

• Need to add #!/bin/bash at the beginning
• To start with # as an explanation
• The name of the script ends with. SH and is used to differentiate between this is a shell script
• There are two methods of executing

Example 01:

[[email protected] shell]# cat 1.sh #!/bin/bashecho "123"

1. chmod +x 1.sh;. /1.sh

[[email protected] shell]# chmod a+x 1.sh[[email protected] shell]# ./1.sh 123

2. Bash 1.sh

[[email protected] shell]# bash 1.sh 123

• View the script execution process bash-x 1.sh

[[email protected] shell]# sh -x 1.sh + echo 123123

• See if the script is syntactically incorrect bash-n 1.sh

[[email protected] shell]# sh -n 1.sh #无错误#只用于检测shell的无法错误

20.3 Date Command usage

Show Current time:

[[email protected] ~]# date2018年 02月 05日 星期一 17:55:33 CST#变更为英文[[email protected] ~]# LANG=en[[email protected] ~]# dateMon Feb  5 17:57:24 CST 2018

• Date +%y-%m-%d,date +%y-%m-%d Month Day

;年[[email protected] ~]# date +%Y2018;取后两位[[email protected] ~]# date +%y18;月份[[email protected] ~]# date +%m02;号（日）[[email protected] ~]# date +%d05;日期[[email protected] ~]# date +%D02/05/18;即[[email protected] ~]# date +%Y-%m-%d2018-02-05;或[[email protected] ~]# date +%F2018-02-05[[email protected] ~]# date +%y-%m-%d18-02-05

• Date +%h:%m:%s = Date +%t time

;时[[email protected] ~]# date +%H18;分[[email protected] ~]# date +%M07;秒[[email protected] ~]# date +%S11;即[[email protected] ~]# date +%H:%M:%S18:06:43;或[[email protected] ~]# date +%T18:08:48

• Date +%s Timestamp

;时间戳[[email protected] ~]# date +%s1517825370

• Date-d @1517825370

#根据时间戳转换成日期[[email protected] ~]# date -d @1517825370Mon Feb  5 18:09:30 CST 2018

• Date-d "+1day" a day later

[[email protected] ~]# date -d "-1 day"Sun Feb  4 18:19:25 CST 2018[[email protected] ~]# date -d "-1 month" +%F2018-01-05

• Date-d "-1 years" a day ago

[[email protected] ~]# date -d "-1 years" +%F2017-02-05

• Date-d "-1 month" month ago

[[email protected] ~]# date -d "-1 month" +%F2018-01-05

• Date-d "-1 min" A minute ago

[[email protected] ~]# date -d "-1 min" +%F2018-02-05

• Date +%w, week date +%w the first few weeks

[[email protected] ~]# date +%w1;是今年的多少周（星期）[[email protected] ~]# date +%W06

• Show Calendar

[[email protected] ~]# cal    February 2018   Su Mo Tu We Th Fr Sa             1  2  3 4  5  6  7  8  9 1011 12 13 14 15 16 1718 19 20 21 22 23 2425 26 27 28

20.4 variables in a shell script

• When a string is used in a script, multiple times and the length of the string is long, you should use a variable instead

• When using conditional statements, use the variable if [$a-gt 1];then ...; Fi

• When referencing the result of a command, replace n= with a variablewc -l 1.txt

• When writing and user interaction scripts, variables are also essential for read-p "Lnput a number:" N; echo $n If you do not write this n, you can use $reply directly

• Built-in variable $0,$1,$2 ... $ A represents the script itself, the first parameter, the second ... $#: Indicates the number of arguments
• Mathematical operations a=1;b=2;c=$ ($a + $b) or $[$a + $b]

Shell script Introduction, script structure and execution, date command usage, variables in scripts