Shell script introduction
Shell is a program written in C language, which is a bridge for users to use Linux. Shell is not only a command language, but also a programming language.
- shell is a scripting language;
- It can use logic judgment, circulation and other syntax;
- Customizable function;
- shell is a collection of system commands;
- shell script can realize automatic operation and maintenance, which can greatly increase our operation and maintenance efficiency;
Shell script structure and execution
structure"ා / bin/bash" is required at the beginning;
The lines beginning with #, in the content of the script, serve as the explanation;
Notes when writing script: author, time, function and other information, convenient to view later;
The name of the script ends with ". sh", which is used to distinguish this is a shell script;
Execution method 1. As an executable program: add the execution permission "chmod a+x test.sh" to the script, and then directly execute the script ". / test.sh"; 2. As interpreter parameter: execute sh test.sh with SH; sh parameter-x: sh -x test.sh view script execution
-n: sh -n test.sh syntax error detected
date command usage
Command description:The date command displays or sets the system time and date.
Command options:-d: Displays the date and time specified by the string (the string must be preceded by double quotes)
-s: Set the time and date according to the string (double quotation marks must be added before and after the string)
[root@dl-001 shell]# date //View current time 2018year 01month 20Saturday, Sunday 10:10:25 CST [root@dl-001 shell]# cal //View system date //January 2018 //Day one two three four five six 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 [root@dl-001 shell]# date +%Y //View current year (four digit display) 2018 [root@dl-001 shell]# date +%y //View current year (simplified display) 18 [root@dl-001 shell]# date "+%Y-%m-%d %H:%M:%S %w" //View current month day hour minute second week 2018-01-20 10:11:15 6 [root@dl-001 shell]# date +%F //View the current full date 2018-01-20 [root@dl-001 shell]# date +%W //View the current week of the year 03 [root@dl-001 shell]# date +%T //View the current time 10:11:39 [root@dl-001 shell]# date +%s //View timestamps (shows the number of seconds that have passed since 00:00:00, January 1, 1970) 1516414309 //Conversion of timestamps [root@dl-001 shell]# date +%s -d "2018-01-20 22:00:00" 1516456800 [root@dl-001 shell]# date -d @1516456800 2018year 01month 20Saturday, Sunday 22:00:00 CST //Print specified date and time [root@dl-001 shell]# date -d "-2 day" +%d 18 [root@dl-001 shell]# date -d "-1 year -3 month -1 day" +%Y-%m-%d 2016-10-19 //Set the current time manually [root@dl-001 shell]# date -s "2017-5-20 12:00:00" 2017year 05month 20Saturday, Sunday 12:00:00 CST [root@dl-001 shell]# date 2017year 05month 20Saturday, Sunday 12:00:03 CST //Synchronize network time [root@dl-001 shell]# yum install -y ntp [root@dl-001 shell]# ntpdate ntp.ubuntu.com 20 Jan 10:47:42 ntpdate[8615]: step time server 91.189.89.198 offset 21163558.201100 sec [root@dl-001 shell]# date 2018year 01month 20Saturday, Sunday 10:47:45 CST