Shulou(Shulou.com)06/03 Report--

Editor to share with you how to use the for sentence and if sentence in the shell script. I hope you will get something after reading this article. Let's discuss it together.

Upper part:

Process oriented:

Sequential execution

Select execute: if, case

Loop execution: for, while, until

I. for statement

Format:

For variable in list; do

Statement 1

Statement 2

...

Done

Example 1. Write a script to add 10 users and make each user's password the same as the user name]

The code is as follows:

#! / bin/bash

For I in {1... 10}; do

Useradd user$I

Echo user$I | passwd-- stdin user$I

Done

Example 2. Write a script that displays the timestamps of the three files / tmp/1.dir / tmp/2.dir / tmp/3.dir, and change the time when the three files were modified to 201003030303.03

The code is as follows:

#! / bin/bash

For Dir in / tmp/1.dir / tmp/2.dir / tmp/3.dir; do

Stat $Dir

Touch-m-t 20100303030303.03$ Dir

Stat $Dir

Done

Variable type of bash:

Local variable

Local variable

Environment variable

Location variables: $1, $2, $3, $4.

Special variables:

$?: used to save the status return value of the command you just executed

0: successful execution; 1-255: failed, 1Pol 2127

You can use the exit command to customize the script execution status return value in the script; if not, the script execution status returns

The return value depends on the state of the last statement executed before the end of script execution

$@, $*: all position parameters

$#: number of location parameters

$0: script name

II. If statement

1. Single-branch if statement:

Format:

If condition; then

Statement 1

Statement 2

...

Fi

Example 3. Write a script to achieve the following functions: if a user exists, it means that it exists

The code is as follows:

#! / bin/bash

UserName=user1

If grep "^ $UserName\ >" / etc/passwd & > / dev/null; then

Echo "$UserName exists."

Fi

Example 4. Write a script to achieve the following functions: if the device / dev/sda3 has been mounted, its mount point is displayed

The code is as follows:

#! / bin/bash

Device='/dev/sda3'

If mount | grep "^ $Device" & > / dev/null; then

Mount | grep "/ dev/sda3" | cut-D''- f3

Fi

Example 5. Write a script to achieve the following function: if there are blank lines in / etc/rc.d/rc.sysinit, the number of blank lines will be displayed

The code is as follows:

#! / bin/bash

File='/etc/rc.d/rc.sysinit'

If grep "^ $" $File & > / dev/null; then

Grep "^ $" $File | wc-l

Fi

2. Double-branch if statement:

Format:

If condition; then

Statement 1

Statement 2

...

Else

Statement 1

Statement 2

...

Fi

Example 6. Write a script to achieve the following functions:

If the device / dev/sda3 is mounted, its mount point is displayed; otherwise, it is not mounted or the device does not exist

The code is as follows:

#! / bin/bash

Device='/dev/sda3'

If mount | grep "^ $Device" & > / dev/null; then

Mount | grep "/ dev/sda3" | cut-D''- f3

Else

Echo "$Device not mounted or not exist."

Fi

3. Multi-branch if statement:

Format:

If condition 1; then

Statement 1

Statement 2

...

Elif condition 2; then

Statement 1

Statement 2

...

Elif condition 3; then

Statement 1

Statement 2

...

Else

Statement 1

Statement 2

...

Fi

Write a script:

Determine the CPU manufacturer of the current host, whose information is on the vendor id line in the / proc/cpuinfo file.

If its manufacturer is GenuineIntel, it shows that it is Intel.

If its manufacturer is AuthenticAMD, it shows that it is AMD.

Otherwise, it will show that it is not recognized

The code is as follows:

#! / bin/bash

Vendor= `grep "vendor_id" / proc/cpuinfo | uniq | cut-d:-f2`

If [[$Vendor = ~ [[: space:]] * GenuineIntel$]]; then

Echo "intel"

Elif [[$Vendor = ~ [[: space:]] * AuthenticAMD$]]; then

Echo "AMD"

Else

Echo "Unknown"

Fi

Lower part:

1. Bash conditional test:

Integer test [expression]

Character test [[expression]]

Conditional test test expression test returns 0 (true) or 1 (false) based on the result of expression evaluation

1. Integer test: numerical comparison

-gt is greater than

-ge is greater than or equal to

-eq equals

-lt less than

-le is less than or equal to

-ne is not equal to

Example 1: write a script to generate two random numbers and compare their sizes; display large numbers

Bash has a built-in variable: $RANDOM

The code is as follows:

#! / bin/bash

A=$RANDOM

B=$RANDOM

If [$A-ge $B]; then

Echo "Max number is $A."

Else

Echo "Max number is $B."

Fi

Example 2: write a script, randomly generate an integer, determine and show its parity

The code is as follows:

#! / bin/bash

#

A=$RANDOM

If [$[$A% 2]-eq 0]; then

Echo "$A: Even"

Else

Echo "$A: Odd"

Fi

Write a script:

Calculate the sum of all odd numbers within 100 and the sum of all even numbers; display them respectively

The code is as follows:

#! / bin/bash

EvenSum=0

OddSum=0

For I in {1... 100}; do

If [$[$I% 2]-eq 0]; then

EvenSum=$ [$EvenSum+$I]

Else

OddSum=$ [$OddSum+$I]

Fi

Done

Echo "EvenSum is: $EvenSum. OddSum is: $OddSum."

Example 4. Calculate the sum of all odd numbers within N and the sum of all even numbers; show them respectively; N is a positive integer passed by parameter

The code is as follows:

#! / bin/bash

EvenSum=0

OddSum=0

For I in `seq 1 $1`; do

If [$[$I% 2]-eq 1]; then

OddSum=$ [$OddSum+$I]

Else

EvenSum=$ [$EvenSum+$I]

Fi

Done

Echo "EvenSum: $EvenSum."

Echo "OddSUm: $OddSum."

Echo "Sum: $[$EvenSum+$OddSum]"

Example 5. Write a script to complete the following requirements:

1. Add 10 users user1, user2,..., user10;, but first determine whether the user exists, do not exist and then add it.

2. After the addition is completed, it shows that a total of several users have been added. Of course, it cannot include those that have not been added because they exist in advance.

3. Finally show how many users there are on the current system

The code is as follows:

#! / bin/bash

Count=0

For I in {1... 10}; do

If id user$I & > / dev/null; then

Echo "user$I exists."

Else

Useradd user$I

Echo "Add user$I successfully."

Count=$ [$Count+1]

Fi

Done

Echo "Add $Count new users."

Echo "Total users: `wc-l / etc/passwd | cut-d'-f1`."

2. Bash character test:

>: greater than

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