2018-4-17 16 weeks 5 Lessons shell script date, if

20.1 Shell Script Introduction

Shell is a scripting language

• Logic Judgments, loops, and other syntax can be used

• Functions can be customized

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

• You need to add #!/bin/bashat the beginning, you can run on this machine, the change machine is not necessarily able to execute. At the beginning of the header, specify which interpreter to run the next command to operate.

• The line that begins 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 twoways to do this: 1,bash or sh sh file; 2, add execute permission to file, then./File

1,bash 1.sh/bin/bash is actually/bin/sh.

[root@localhost shell]# ll /bin/bash
-rwxr-xr-x. 1 root root 960472 8月   3 2017 /bin/bash
[root@localhost shell]# ll /bin/sh
lrwxrwxrwx. 1 root root 4 12月 28 05:37 /bin/sh -> bash

2, have the executive permission, chmod +x 1.sh; can be directly./1.sh

3, in fact, the absolute path of the direct input file can also be executed

[root@localhost shell]# /root/shell/01.sh
123
22:22:27 up 2:21, 1 user, load average: 0.02, 0.02, 0.05
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
Root pts/0 192.168.65.1 20:08 3.00s 0.06s 0.00s /bin/bash /root/shell/01.sh
Total usage 4
-rwxr-xr-x 1 root root 32 April 16 22:22 01.sh

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

[root@localhost shell]# sh -x 01.sh
+ echo 123
123
+ w
22:23:55 up 2:23, 1 user, load average: 0.00, 0.01, 0.05
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
Root pts/0 192.168.65.1 20:08 3.00s 0.07s 0.00s sh -x 01.sh
+ ls -l
Total usage 4
-rwxr-xr-x 1 root root 32 April 16 22:22 01.sh

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

Deliberately write the wrong script (random characters are not error)

[root@localhost shell]# sh -n 01.sh
01.sh: Line 10: Syntax error: Unexpected end of file

20.3 Date command usage

[[email protected] ~]# date
2018 April 17 Tuesday 20:15:04 CST

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

[root@localhost ~]# date +%Y-%m-%d
2018-04-17
[root@localhost ~]# date +%y-%m-%d
18-04-17
[root@localhost ~]# date +%d ## d Date
17
[root@localhost ~]# date +%D ## US format year, month, day
04/17/18
[root@localhost ~]# date +%M ## M minutes
06
[root@localhost ~]# date +%m ## m month
04
[root@localhost ~]# date +%F ## Date
2018-04-17

Date +%h:%m:%s = Date +%t time

[root@localhost ~]# date +%H:%M:%S
21:29:15
[root@localhost ~]# date +%T
21:29:35
[root@localhost ~]# date +%H ##hour
twenty one
[root@localhost ~]# date +%h ##month (with format, set Chinese is April, English is Aprl)
April
[root@localhost ~]# date +%M ##minutes
31
[root@localhost ~]# date +%m ##month
04
[root@localhost ~]# date +%S ##seconds
44
[root@localhost ~]# date +%s ##timestamp
1523971907

Date +%s time stamp

How many seconds from 1970-01-01-00-00-00 past

date +%w, date +%w Week

[[Email protected] ~]# date +%w## weeks 2[[email protected] ~]# date +%w## The week of this year 16

date-d @1504620492

[root@localhost ~]# date +%w## Day of the week
2
[root@localhost ~]# date +%W## The first few weeks of the year
16

date-d "+1day" a day later

[root@localhost ~]# date -d @1504620492##Know the timestamp to check the date
Tuesday, September 05, 2017 22:08:12 CST
[root@localhost ~]# date +%s -d "2018-4-17 21:52:30"##Know the date to check the timestamp
1523973150 

date-d "-1 days" a day ago

date-d "-1 month" Month ago # #年year

[Email protected] ~]# date-d "-1 month" +%F2018-03-17

date-d "-1 min" A minute ago # #小时hour, seconds second

[[email protected] ~]# date-d "-1 min" +%t21:47:09

[[email protected] ~]# cal April 2018 1,234,561 2 3 4 5 6 78 9 10 11 12 13 1415 16 17 18 19 20 2122 23 24 25 26 27 2829 30

20.4 variables in a shell script

• 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, use the variable if [$a-gt 1]; Then ...; Fi

• Replace n= ' wc-l 1.txt ' with a variable when referencing the result of a command

• When writing and user interaction scripts, variables are also essential for read-p "Input a number:" N; Echo $n If you don't write this n, you can use $reply directly.

• Built-in variables $, $ $, $ ... $ $ represents the script itself, the first parameter, the $ A second ... $ #表示参数个数

• Mathematical operations a=1;b=2; c=$ (($a + $b)) or $[$a + $b]

2018-4-17 16 weeks 5 Lessons shell script date, if