Shell scripting improves

Shell scripting improves

Date//view dates and times

-S change Time date-s "2015-08-20 14:27:12"

View time Date + "%y-%m-%d%h:%m:%s"

-D Change Single time Date-d "-2 Days" +%f

+%w Show weeks

+%w show how many weeks this year

ntpdate //Calibration time ntpdate ntp.fudan.edu.cn use Fudan University server proofing time. Need to install NTP package

cal //view calendar of the month

-y view calendar throughout the year

Built-in variables

The first parameter

$ A second parameter

$ A script itself name

$# Number of parameters

Common symbols

>-gt greater than

=-eq equals

<-lt less than

! =-ne Not equal to

>=-ge greater than or equal to

<=-le less than or equal to

-F is set when it is a file

-D is established when it is a directory

-R set up when the file is readable

-W When the file can be written to be established

-X when the file executable is established

-N When the variable is not empty, set up

-Z When the variable is empty

If statement

First Kind

If condition judgment

Then

Results

Fi

The second Kind

If condition judgment

Then

Results

Else

Results

Fi

Third Kind

If condition judgment

Then

Results

Elif

Then

Results

Else

Results

Fi

Case statement

Case parameter in

Condition judgment)

Results

;;

Condition judgment)

Results

;;

*)

Results

;;

Esac

For statement

SEQ//command to generate sequence

SEQ 1 10//Display sequence

SEQ 1 2 10//Set step

SEQ 10-2 1//Reverse

seq-w 01 10//Plus-W parameter sets the number of sequence bits by the maximum number width

The for reference variable in condition is judged

Do

Output results

Done

While statement

In an uninterrupted loop statement, ":" Is always true

While condition judgment

Do

Results

Done

Break continue exit statement

Break//End entire loop

Continue//end of this cycle

Exit//End the entire shell directly

Function can be thought of as a fragment of a shell, or a small unit

Function name () {

Statement

}

Function name (call)

Local//Use local variables, only in child functions

function can be omitted

Array

A= (1 2 3 4)//define Array

echo ${a[@]}//display array

echo ${a[*]}//Replace @ with * can also output array

echo ${a[0]}//Output first digit

a[2]=7//Change a number

echo ${#a [*]}//Plus # statistics total

Random number four-bit or five-bit

echo ${a[@]:0:4}//print four random numbers

Shell scripting improves