Part Three Shell programming 3 (Shell Scripting 1)

Do monitoring and backup up to

1. What is a shell script?
It's a scripting language, not a programming language.
You can use some logical judgments, loops, and other syntax
You can customize the sub-function
is a collection of system commands
Shell scripts enable automated operations, greatly increasing our productivity

first shell script:
mkdir shell
" Span style= "font-size:15px;" >CD shell/
vim 1.sh
"
' #!/bin/bash
#This is a test shell Script
'
echo" 123456. "
"Touch aming.111

2. Shell script structure and execution methods
Start line Specify Bash path: #! /bin/bash
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 ways of execution: chmod +x 1.sh;./1.sh
Bash 1.sh If you don't have Execute permissions
can also sh 1.sh can view ls-l/bin/sh

Bash-x 1.sh To view the script execution process

Cal output Calendar.
CAL-Y output year-round calendar

lang=en

3. Learn the usage of the date command
Date +%y-%m-%d, date +%y-%m-%d, date +%f Month Day
Date +%h:%m:%s = Date +%t time

Date +%s Timestamp
Date-d "+1day" a day later
Date-d " -1day" a day ago
Date-d " -1day" +%f what was the date a day ago?
Date-d " -1month" month ago

Date-d " -1hour" an hour ago
Date-d " -1hour" +%t an hour before the time is how much, the following several like

Date-d " -1min" a minute ago
Date-d " -1sec" a second ago
Date +%w, week date +%w week of the year, 52 weeks in a year

The time to run this script to generate a log, saved in the TMP directory
Vim 2.sh
#! /bin/bash
d= ' Date +%t '
Logname= $d. Log
touch/tmp/$logname

This is the log for the TMP.

BC is calculator
One is the direct input transport
An echo "365/7" |BC

4. 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
Variables are essential when using conditional statements
When referencing the result of a command, replace it with a variable
Variables are also necessary when writing scripts for user interaction
Built-in variables, $ ...
Mathematical Operation a=1;b=2; c=$ (($a + $b)) or $[$a + $b]

echo "SCALE=2;5/2" |BC output is 2.50

Vim 3.sh
#! /bin/bash
Read-p "Pleaswe input number" n
Echo $n

========
Read-t 3-p "Pleaswe input number" N T is the time-out
===============

Vim 4.sh
#! /bin/bash
Echo
echo $
Echo

Input parameters of the time of the output is itself 4.sh

Vim 5.sh
#!/bin/bash
n1=0
While :;: denotes true meaning, or it can be 1
Do
read-p "Please inpty a number:" N
m= ' echo $n |sed ' s/[0-9]//g ' m is to remove all the numbers and decide if it's empty .
l= ' echo $m |wc-c ' If it's a pure number, it's definitely empty, l if it doesn't range.
if [$l! = "1"]; then 1 is not empty and must contain numbers or pure letters
echo "The charater you input was not a number."
n1= ' echo ' $n "|BC ' l if not equal to 1, record him once.
Else
echo "Your number is $n" if the pure digit description is empty on the output, then exit
Exit 0
fi
if [$n 1 = = "5"];then exit if the input is not a number more than 5 times
Exit 1
fi
Done

--------------
A=
echo $a |wc-c C is a couple of strings
The output is 1 for the null character, because he has a line break

echo "12345a" |sed ' s/[0-9]//g ' here output is a

echo "12345" |sed ' s/[0-9]//g ' Here the output is empty

5. Shell

format 2:if condition; then statement; Else statement; Fi
format 3:if ...; Elif ...; Then ...; else ...; Fi
logical judgment expression: if [$a-gt $b]; if [$a-lt 5]; if [$b-eq 10]

-GT (>); -lt (<); -ge (>=); -le (<=);-eq (= =); -ne (! =) Note that there are spaces everywhere
can use && | | Combine multiple conditions
N=5
If [$n-gt 2] && [$n-lt 10]; then echo OK; else Echo Nook;fi
=
If [$n-gt 2-a $n-lt 1]; then echo OK; else Echo Nook;fi

-A is with the meaning
=========================
If [$n-gt 2] | | [$n-lt 1]; then echo OK; else Echo Nook;fi
=
If [$n-gt 2-o $n-lt 1]; then echo OK; else Echo Nook;fi

-O is or means

=========================
Format 1 and Format 2
Vim 6.sh
#! /bin/bash
n=10
If [$n-GT 5]
Then
echo "Greater than 5"
Else
echo "Not greater than 5"

Fi

======================
Format 3
Vim 6.sh
#! /bin/bash
N=3
If [$n-GT 5]
Then
echo "Greater than 5"
elif [$n-lt 2]
Then
echo "Less than 2"
Else
echo "Greater than 2"

Fi

6. If determine file, directory properties
[-F file] Determines if it is a normal file, and there is
[-D file] Determines if it is a directory and exists
[-e File] Determines whether the files or directories exist ======
[-R File] to determine if the document is readable
[-W file] Determines whether the file is writable
[-X file] Determines whether the file is executable

echo $RANDOM generate a random number
Echo $RANDOM $random
echo $RANDOM $random$random |cut-c 1-10 as long as the first 10 bits
Or
mkpasswd
Mkpasswd-l 20
Mkpasswd-l 20-s 0 Special symbols
Mkpasswd-l 20-s 0-c 0-c 0

Part Three Shell programming 3 (Shell Scripting 1)