Shell Footstep Writing

1.shell scripts are a collection of commands. Record a set of commands that need to be executed to the document, and then call the document.

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Shell Footsteps Writing recommendations: Custom scripts placed in the/usr/local/sbin directory

2. First shell script

Vim firstshell.sh

#! /bin/bash

# #this is my first shell script

# #writen by Jason 2015-07-02

Date

echo "Hello world!"

#! /bin/bash, which begins with the first line, indicates that the file uses bash syntax

. sh suffix, habit

#后面跟的注释, good habits, easy to see footsteps later

Execute script: Sh firstshell.sh or./firstshell.sh (sometimes chmod modified when a permission is missing)

3. use of variables in scripts

VI variable.sh

#! /bin/bash

# in Thie shell script we'll use variables

# # Writen by Jason 2015-07-02

d= ' Date +%h:%m:%s '

echo "This script begin at $d"

echo "Now we'll sleep 2 seconds."

Sleep 2

d1= ' Date +%h:%m:%s '

echo "This script end at $d 1"

Variables d and D1 are defined using anti-quote ' ', variable content used to the results of other commands (Shell Footstep Basics blog).

Script total reference variable, plus $

3.1 numeric operations , two-digit sum

VI sum.sh

#! /bin/bash

# # Sum of tow numbers

# by Jason 20150702

A=1

b=2

sum=$[$a + $b]

Echo $sum

Mathematical calculation, to be enclosed in [], and the outermost to add a $

3.2 User interaction , user input

VI read.sh

#! /bin/bash

# # Use ' read ' in shell script

# by Jason 20150702

Read-p "Please input a number:" X

Read-p "Please input anoter number" Y

sum=$[$x + $y]

echo "The sum of the number is: $sum"

read is used to interact with the user and use the user input string as the variable value

-X View the shell execution process, sh-x read.sh

3.3 Shell preset variable $1,$2,$0 (the name of the print script itself)

VI option.sh

#! /bin/bash

##

##

SUM=$[$1+$2]

Exho "Sum= $sum"

SH option.sh 3 7

sum=10

$1,$2 is the shell footstep preset variables, by default, enter two numbers sequentially, the default assignment variable $1=3,$2=7.

The same $3,$4,$5 is a preset variable in turn.

4. logic in the script to determine if, if...else,if. Elif. Else

4.1 VI iftest1.sh

#! /bin/bash

##

##

Read-p "Input Your score:" A

if (($a <60)); Then if Judgment statement; Then

echo "didn ' t pass the exam." Commond

Fi fi

(($a <60)), a unique format in the shell's footsteps, must use two ()

Syntax format: if judgment statement; then

Match the result to execute the corresponding command

4.2 If. Else

VI iftest2.sh

#! /bin/bash

##

##

Read-p "Iput Your score:" A

if ($a <60)); then if Judgment statement; Then

echo "Do not pass." Commond

else Else

echo "Good!                  Pass the exam. " Commond

Fi fi

4.3 If. Esif. Else

VI iftest3.sh

#! /bin/bash

##

##

Read-p "Input Your score:" A

if (($a <60)); Then

echo "Do not pass."

Elif ($a >=60) && (($a <80)); Then

echo "Good,pass."

else echo "Very Good,high."

Two judgment statements by && or | | Together, Two (()) must be separated and judged individually

Determine the value in addition to (()) Form, there is [], but need -lt (less than),-GT (greater than),-le (less than equals),-ge (greater than or equal),-eq (equals),-ne (not equal)

If [$a-lt 60]; Then

If [$a-gt 60] | | [$a-lt 80]; Then ....

4.4 Determining document properties

-E to determine whether a file or directory exists;-D to determine if it is a directory and exists;-F to determine if it is a normal file and exists

;-R Determines whether the document is readable, if-w is feasible, and-X is executable.

if [-f/root/test.txt]; Then echo, "It is file."; Fi

[] must add a space before and after, or error.

5. Script Logic judgment case

VI case.sh

#! /bin/bash

##

##

Read-p "Input a number:" N

a=$[$n%2]

Case $a in case variable in

1) value1)

echo "The number is odd." Commond

;; ;;

0) value2)

echo "The number is even." Commond

;; ;;

*)

echo "This was not a number"

;;

Esac

The number of value values is not limited to judgment.

6. the loop for in the script

VI fortest.sh

#! /bin/bash

For i in ' SEQ 1 5 '; Do for variable name in loop condition; do

echo $i Command

Done

Loop condition SEQ 1 5 represents a sequence from 1-5

The 6.1 loop condition is written as a set of strings or numbers, or it can be a result of a command execution

For I in 1 2 3 4 a B; do echo $i; Done

For file in ' ls '; do echo $file; Done

7. loops in the script while

VI whiletest.sh

#! /bin/bash

A=5

While [$a-ge 1]; Do and loop condition;

echo $a command

a=$[$a-1]

Done

8.Functions in shell scripts

Function: is to organize a piece of code into a small unit, a name, call the name of the unit.

VI func.sh

#! /bin/bash

function sum () function name ()

{                             {  

Sum=$1+$2 Command

Echo $sum

}                            }

Sum $ $ Call function

In a shell script, the function must be written first, not in the back or in the middle, and in the first declaration, before it can be called later.

Shell Footstep Writing