Introduction to shell scripting for Linux, shell script structure and execution, date command usage, variables in shell scripts

Shell Script Introduction

• 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

Shell script structure and execution

• Need to add #!/bin/bash at the beginning
• Lines that begin with # are interpreted as explanatory notes
• The name of the script ends with. SH and is used to differentiate between this is a shell script
• There are two methods of execution, plus execute permission chmod +x 1.sh;1. ./1.sh2. /root/shell/01.sh (absolute path execution)
• Execute Script Bash 1.sh
• View the script execution process bash-x 1.sh
• See if the script is syntactically incorrect bash-n 1.sh

Practice a script to do the testing:

[[email protected] ~]# mkdir shell[[email protected] ~]# cd shell/[[email protected] shell]# ls[[email& Nbsp;protected] shell]# vi 01.sh[[email protected] shell]# bash 01.sh 123 10:57:41 up 9 min, 1 user, load average: 0.00, 0.13, 0.13USER TTY from [email protected] IDLE jcpu PCPU whatroot pts/0 172.1 6.111.1 10:49 5.00s 0.03s 0.01s w01.sh[[email protected] shell]# cat 01.sh #!/bin/bash//First line this if you do not write on this side, Line script when added/bin/bsah can echo "123" wls[[email protected] shell]# chmod a+x 01.sh [[email protected] shell]#./01.sh   123 10:58:12 up 9 min, 1 user, load average:0.00, 0.11, 0.12USER TTY from [email protected] IDLE jcpu PCPU whatroot pts/0 172.16.111.1 10:49 4.00s 0.02s 0.00s/bin/bash./01.sh01.sh[[email&nbsp ;p rotected] shell]# ls-l/bin/bash-rwxr-xr-x. 1 root root 960392 August 3 2016/bin/bash[[email protected] shell]# ls-l/bin/shlrwxrwxrwx. 1 root RooT 4 October 05:04/bin/sh-bash[[email protected] shell]#/bin/bash 01.sh 123 11:02:12 up min, 1 user, load     average:0.00, 0.05, 0.10USER TTY from [email protected] IDLE jcpu PCPU whatroot pts/0 172.16.111.1 10:49 4.00s 0.03s 0.00s w01.sh# View script execution process [[email protected] shell]# bash-x 01.sh + echo 1231 23+ W 11:12:04 up min, 1 user, load average:0.00, 0.03, 0.07USER TTY from [email protected ] IDLE jcpu PCPU whatroot pts/0 172.16.111.1 10:49 4.00s 0.04s 0.01s w+ ls01.sh# Check for script syntax error [[EMAIL&NBSP ;p rotected] shell]# bash-n 01.sh [[email protected] shell]#/root/shell/01.sh 123 11:23:45 up min, 1 user, lo Ad average:0.05, 0.05, 0.06USER TTY from [email protected] IDLE jcpu PCPU whatroot PT s/0 172.16.111.1 10:49 1.00s 0.05s 0.00s/bin/bash/root/shell/01.sh01.sh

Use of the date command

• Basic usage List

 date??+%Y-%m-%d, date +%y-%m-%d 年月日 date??+%H:%M:%S = date +%T 时间 date +%s??时间戳 date -d @1504620492 date -d "+1day"  一天后 date -d "-1 day"  一天前 date -d "-1 month" 一月前 date -d "-1 min"  一分钟前 date +%w, date +%W 星期

• Usage examples

[[email protected]]# date2018 February 03 Saturday 13:41:51 cst# Display the date command into English [[email protected]]# Lang=en[[email  protected]]# Datesat Feb 3 13:45:14 CST 2018# year [[email protected] ~]# date +%y2018# Two-bit year [[email protected ] ~]# date +%y18# month [[email protected] ~]# date +%m02# minutes [[email protected] ~]# date +%m47# dates [[email  Protected] ~]# Date +%d03[[email protected] ~]# date +%d02/03/18[[email protected] ~]# date +%y%m%d20180203[[ Email protected] ~]# date +%f2018-02-03# hour [[email protected] ~]# date +%h13# second [[email protected] ~]# Date +%s41# timestamp (distance 19700101 past number of seconds) [[email protected] ~]# date +%s1517636984[[email protected] ~]# date-d @ 1517637599Sat Feb 3 13:59:59 CST 2018[[email protected] ~]# date +%s-d "2018-02-03 13:59:59" 1517637599# time [[EMAIL&NB Sp;protected] ~]# date +%t13:52:05[[email protected] ~]# date +%h:%m:%s13:53:17# English month [[email protected] ~]# Date +%hfeb# Day of the week [[email protected] ~]# date +%w6# the week of the year [EMail protected] ~]# date +%w05# display calendar [[email protected] ~]# cal February 2018 Su Mo Tu We Th Fr Sa 1 2 3 4 5 6 7 8 9 1011 1718 (2425) 28[[email protected] ~]# date-d "+1 da Y "Sun Feb 4 14:02:19 CST 2018[[email protected] ~]# date-d"-1 day "Fri Feb 2 13:57:49 CST 2018[[email protect Ed] ~]# date-d "-1 day" +%f2018-02-02[[email protected "~]# date-d"-1 month "+%f2018-01-03[[email protected] ~]# date-d "-1 year" +%f2017-02-03[[email protected "~]# date-d"-1 Hour "+%t12:59:07

Variables in shell scripts

• You should use a variable instead when you use a string more frequently in your script and the string length is long
• When using conditional statements, variables are often used?? If [$a-gt 1]; Then ...; Fi
• When referencing the result of a command, replace it with a variable?? n=wc -l 1.txt
• When writing scripts for user interaction, variables are also necessary?? Read-p "Input a number:" N; echo $n?? If you don't write this n, you can use $reply directly.
• Built-in variables, $ $, $ ...? ? $ A represents the script itself, the first parameter, the second ...? ?? ? $ #表示参数个数
• Mathematical Operation a=1;b=2; c=$ (($a + $b)) or $[$a + $b]

Introduction to shell scripting for Linux, shell script structure and execution, date command usage, variables in shell scripts