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

Basic script programming of bash and shell

Command execution with many bash features: separated by semicolons, no relationship between commands

] # cmd

Method 1:] # cmd1 `cmd2`: command reference to achieve multiple commands

Method 2:] # cmd1 | cmd2 | cmd3 |.: pipeline implements multiple commands

Method 3:] # cmd1;cmd2;cmd3;...: semicolon to achieve multiple commands

Logical combination: the operation is the running status of the command and the result is the exit code.

] # cmd1 & & cmd2 & &...

] # cmd1 | | cmd2 | |.

] #! cmd1

Exit code:

0: expressed as true, true, success, successful

1-255: represented as failure, false, error

Logical operation: the main operation is the running status of the command, that is, the exit code.

It can be thought that there is a judgment mechanism in it; the judgment depends on whether it is related to the operation or the operation also depends on the result of the first operation.

Operands: true (1), false (0)

COMMAND running status results:

0:TRUE, successful

1-255:FALSE, error

And: see false (0) is false (0); equivalent to multiplication

True & & true = true

True & & false = false

The first Operand is true, and the result depends on the second Operand

False & & true = false

False & & false = false

The first Operand is false, and the result can be determined to be false

For example:

] # ls / var & & cat / etc/fstab

] # lls / var & & cat / etc/fstab

Or: see true (1) for true (1); equivalent to addition

True | | true = true

True | | false = true

The first Operand is true, and the result can be determined to be ture

False | | true = true

False | | false = false

The first Operand is false, and the result depends on the second Operand

For example:

] # id hive | | useradd hive: if the user does not exist, add the user

] # id hive

Non: inverted

! True = false

! Fase = true

For example:

] #! Id hive & & useradd hive: if the user does not exist, add the user

Priority: non (high) / dev/null | | useradd user2

User1_id=$ (id-u user1)

User2_id=$ (id-u user2)

Id_sum=$ [$user1_id+$user2_id]

Echo "the id sum: $id_sum"

Enhanced variable assignment:

+ =,-=, * =, /,% =

Itself equals itself + numeric value, use the let command

For example:

] # declare-iitem1

] # iTunes $[$item1]

] # echo $I

Enhanced assignment is now available:

] # let iTunes 1

The variable is saved back to this variable after doing some arithmetic operation

Let i=$i+#

Let iTunes #

#: representative number

Self-increasing:

VAR=$ [$VAR+1]

Let VAR+=1

Let VAR++

Self-subtract:

VAR=$ [$VAR-1]

Let VAR-=1

Let VAR--

Exercise:

1. Script implementation to calculate the sum of the ID numbers of the 15th user and the 18th user in the / etc/passwd file

Decompose: do the calculation of 2 id numbers, id_sum=$ [$id1+$id2]

$(head-15 / etc/passwd | tail-1 | cut-d:-f3)

Baked $(head-18 / etc/passwd | tail-1 | cut-d:-f3)

Sum=$ [$axifolb]

Echo "the an is:$a"

Echo "the b is: $b"

Echo "teh sum is: $sum"

2. Calculate the sum of blank lines in / etc/rc.d/init.d/functions and / ect/inittab files

$(egrep "^ [[: space:]] * $" / etc/rc.d/init.d/functions | wc-l)

$(egrep "^ [[: space:]] * $" / etc/rc.d/init.d/network | wc-l)

Sum=$ [$axifolb]

Echo "an is: $a"

Echo "b is $b"

Echo "sum is: $sum"

Conditional testing for bash scripting:

To judge whether a requirement is met or not, it needs to be realized by the testing mechanism.

How to write test expressions to implement the required tests:

For example, to judge whether a file has blank lines or whether a user exists.

(1) execute the command and use the return value of the command status to judge

0: successful

1-255: failed

$?: stores the return value of the execution status of the previous command

For example:

Determine whether the user centos is logged in to the system:

Who | grep "^ centos\ >"

Echo $?: displays the return value of the previous command status

Get the return value of command status. 0: login, 1-255: not logged in

(2) Test expression

Test EXPRESSION

[EXPRESSION]

`EXPRESSION'

When comparing characters, use double parentheses

Note: there must be white space characters at both ends of the EXPRESSION, otherwise the syntax is wrong.

Test types for bash scripting:

Numerical test

String test

File testing

Numerical testing: comparison between numerical values

-eq: whether it is equal to; for example: [$num1-eq $num2], test 2-eq 3 or [2-eq 3]

-ne: is it not equal to

-gt: whether it is greater than

-ge: whether it is greater than or equal to

-lt: whether it is less than

-le: whether less than or equal to

For example:

] # test 2-gt 3

] # [$A-eq $B]

Exercise:

Is the id of centos users larger than the ID of ubuntu users?

Await $(id-u centos)

Baked $(id-u ubunto)

[$a-gt $b] & & echo "centos is bigger" | | echo "ubuntu is bigger"

String test comparison

=: whether it is equal to or equal to true

! =: whether it is different or not does not mean it is true

>: whether it is greater than, greater than is true

/ dev/null | | useradd mageedu & & exit 5

Or: id mageedu & > / dev/null & & exit 5 | | useradd mageedu

Bash script programming passes parameters to the script

Position parameter variable

Command line: * .sh argu parameter 1 argu parameter 2 argu parameter 3.

Quote in the script: $1 $2 $3.

Myscript.sh agru1 argu2...

Citation method:

$1: save argu parameter 1

$2: save argu parameter 2

...

${10}, ${11}.

Rotation:

Shift [n]: position parameter rotation. N is the number and defaults to 1. It is expressed as the first few parameters of a rotation.

$1 for 2. It is called position parameter variables, and the values of these parameter variables are changed by passing parameter changes each time the script is run.

For example:

My_shell.sh ubuntu centos linux

Citation method:

Use $1 in the script "2" 3

Useradd $1

Useradd $2

Useradd $3

Explanation: $1 ubuntu, 2 century, 3 Linux.

Shift #: delete the specified parameter; add the following parameters to the front

Exercise:

Script implementation, passing two text paths to the script through the command to calculate the sum of its blank lines (^ $)

$(egrep "^ $" $1 | wc-l)

Baked $(egrep "^ $" $2 | wc-l)

Sum=$ [$axifolb]

Echo "an is: $a"

Echo "b is $b"

Echo "sum is: $sum"

Shift #: automatically kicks out command parameters

Special variables:

$0: save the script file path itself

$#: the number of script parameters saved

$*: save all parameters; display each parameter as an independent parameter

$@: save all parameters; put each parameter together and display it as a string parameter

$0: indicates the path of the script file given by the command line

For example: command line] # bash / tmp/parameter_blanksum.sh

Script content: echo $0

The display result is: / tmp/parameter_blanksum.sh

If the command line is: bash parameter_blanksum.sh

The content of the script remains unchanged, and the display result is: parameter_blanksum.sh

$#: indicates the number of script parameters

For example:

] # bash parameter_blanksum.sh / etc/init.d/functions / etc/init.d/network

Script content: echo $#

The display result is: 2

$*: indicates that the parameter is multiple strings

$@: indicates that the parameter is a string

For example: command line] # bash parameter_blanksum.sh / etc/init.d/functions / etc/init.d/network

Script content: echo $*

Echo $@

The display result is: / etc/init.d/functions / etc/init.d/network

/ etc/init.d/functions / etc/init.d/network

But $* is represented as two separate paths, while $@ is represented as an entire behavior and a string.

Exercise:

1. Determine whether / etc/passwd is a file. If it is a file, output / etc/passwd is files. The path is passed through commands. When the number of commands passed in is greater than 1, an error is reported.

[$#-gt 1] & & echo "something wrong" & & exit

[- f $1] & & echo "/ etc/passwd is files"

2. Write a script in the root directory and add 3 users at once. You can add users by passing parameters. If the passed parameters do not match 3, an error will be reported.

When the three users are added, the script needs to be reinforced (lock mechanism, which can no longer be executed), and the permissions of the script need to be changed to owner readable, writable and executable.

! [$#-eq 3] & & echo "please give me three username" & & exit 1

Useradd $1 & & axi1

Useradd $2 & & baked 1

Useradd $3 & & Clear1

Sum=$ [$a+$b+$c]

[$sum-eq 3] & & echo "$1 $2 $3" | | exit 2

Chmod 7000.00

Echo $1 is added

Echo $2 is added

Echo $3 is added

Echo "this scripts mode is 700"

Or:

[$#-gt 3] | | [$#-lt 3] & & echo "something wrong,give three user" & & exit 1

Id $1 & > / dev/null & & echo "$1 exist" | | useradd $1

Id $2 & > / dev/null & & echo "$2 exist" | | useradd $2

Id $3 & > / dev/null & & echo "$3 exist" | | useradd $3

Echo "three users $1, 2, 3, are added success"

Chmod 7000.00

Echo "this script mode is 700"

The code execution order of the procedural programming language:

Sequential execution: run one by one

Select execute:

There is a branch of the code: it will not be executed until the condition is met.

Two or more branches: only one of the branches that meets the criteria will be executed

Loop execution:

A code snippet (loop body) to perform 0, 1 or more back and forth (loop)

Sequential execution

Condition selection:

(1) &, | |

(2) if statement (single branch, double branch, multi-branch)

(3) case statement

Loop execution: for,while,until

If statement selection Branch of bash script programming

Condition judgment:

Shell execution is executed sequentially

Select Branch

Single branch if statement

If test condition; then (if the condition is true, execute the following statement)

Code branch

Fi

Or

If test condition

Then

Code branch

Fi

Double-branched if statement

If test condition; then

Branch executed when the condition is true

Else

Branch executed when the condition is false

Fi

Multi-branch if statement

If test condition; then

Branch executed when the condition is true

Elif test condition; then

Elif test condition; then

Elif test condition; then

Else

A branch that is executed when the condition is false

Fi

For example:

Pass a user name to the script through the parameter, and create the user if the user does not exist

If! Grep "^ $1\ >" / etc/passwd & > / dev/null;then

Useradd $1

Echo $1 | passwd-- stdin $1 & > / dev/null

Echo "add a user $1 finished"

Else

Echo "$1 is exist"

Fi

Example: pass a user name to the script through the parameter, and add it when the user does not exist. (to judge the expression: one is a command, the other is that the expression is placed in square brackets or represented by test to determine whether the user exists with id or grep)

~] # vim useradd.sh

If! Grep "^ $1\ >" / etc/passwd & > / dev/null;then

Useradd $1

Echo $1 | passwd-- stdin $1 & > / dev/null

Echo "add user $1 finished"

Fi

~] #. / useradd.sh hbase

The execution result is: add user hbase finished

A judgment if statement is added to determine whether the parameter exists or not:

~] # vim useradd.sh

If [$#-lt 1]; then

Echo "at least one username"

Exit 2

Fi

If! Grep "^ $1\ >" / etc/passwd & > / dev/null;then

Useradd $1

Echo $1 | passwd-- stdin $1 & > / dev/null

Echo "add user $1 finished"

Fi

~] #. / useradd.sh hbase

Change to a two-branch judgment if statement:

~] # vim useradd.sh

If [$#-lt 1]; then

Echo "at least one username"

Exit 2

Fi

If grep "^ $1\ >" / etc/passwd & > / dev/null;then

Echo "user $1 exists"

Else

Useradd $1

Echo $1 | passwd-- stdin $1 & > / dev/null

Echo "add user $1 finished"

Fi

~] #. / useradd.sh hbase

Exercise:

1. Through the command parameters, two numbers are given, and the larger number is output.

If [$1-gt $2]; then

Echo $1 is bigger

Else

Echo $2 is bigger

Fi

Or:

If [! $#-eq 2]; then

Echo "give two number"

Exit 2

Fi

If [$1-gt $2]; then

Echo "the bigg is $1"

Elif [$1-lt $2]; then

Echo "the bigg is $2"

Else

Echo "$1 million 2"

Fi

2. Through the command parameter, two text file names are given, and if a file does not exist, the script ends. If there is a number of lines returned to each file, and echo the file name with more lines.

[$#-ne 2] & & echo "give two file" & & exit 1

If! [- e $1]; then

Echo "$1 is not find"

Exit 2

Elif! [- e $2]; then

Echo "$2 is not find"

Exit 3

Fi

F1 dollars (cat $1 | wc-l)

F2salary $(cat $2 | wc-l)

Echo "$1 line is $F1"

Echo "$2 line is $f2"

If [$F1-gt $f2]; then

Ehco "$F1 is more"

Elif [$F1-eq $f2]; then

Echo "F1 and f2 the same"

Else

Echo "$f2 is more"

Fi

Or:

If! [$#-eq 2]; then

Echo "give 2 files"

Exit 20

Elif! [- e $1]; then

Echo "$1 is not exist"

Elif! [- e $2]; then

Echo "$2 is not exist"

Exit 30

Else

F1 dollars (cat $1 | wc-l)

F2salary $(cat $2 | wc-l)

Echo "f1=$f1"

Echo "f2=$f2"

Fi

If [$F1-gt $f2]; then

Echo "file1 line is more: $F1"

Echo "$(basename $1) line is more"

Elif [$F1-lt $f2]; then

Echo "file2 line is more: $f2"

Echo "$(basename $2) line is more"

Else

Echo "f1-$f1 and f2-$f2 is same"

Fi

3. Give a user name through the command line parameter to determine whether the ID number is even or odd.

Multi-branch if statement

Select execute:

(1) &, | |

(2) if statement

(3) case statement

If statement: three formats

Single branch if statement

If CONDITION;then

If-ture- branch

Fi

Double-branched if statement

If CONDITION;then

If-true- branch

Else

If-false- branch

Fi

Multi-branch if statement

If CONDITION1;then

Condition 1 is a true branch.

Elif CONDITION2;then

Condition 2 is a true branch.

Elif CONDITION3;then

Condition 3 is a true branch.

...

Elif CONDITIONn;then

Conditional nweizhen bifurcation

Else

Branch when all conditions are not met

Fi

Note: even if multiple conditions may be met at the same time, the branch will only execute one of them. After the conditional branch whose first test is true is executed, it will exit.

Example: pass the file path to the script to determine the type of the file through the script parameters

If [$#-lt 1]; then

Echo "at lease one path"

Exit 1

Fi

If! [- e $1]; then

Echo "no such file"

Eixt 2

Fi

If [- f $1]; then

Echo "common file"

Elif [- d $1]; then

Echo "directory file"

Elif [- L $1]; then

Echo "symbolic link file"

Elif [- b $1]; then

Echo "block special file"

Elif [- p $1]; then

Echo "pipe file"

Elif [- S $1]; then

Echo "socket file"

Elif [- c $1]; then

Echo "character special file"

Case statements are actually simplified versions of multi-branch if statements, but not all if statements can be converted into case statements

Note: if statements can be nested to use

Exercise:

1. Write scripts to achieve the following functions:

(1) pass a parameter to the script, which is the user name

(2) judge the type of user according to its id

0: administrator

1-999: system user

1000 hours: login user

(3) if it does not exist, you can add this user.

[$#-lt 1] & & echo "at least one username" & & exit 1

! Id $1 & > / dev/null & & echo "no such user" & & exit 2

Userid=$ (id-u $1)

If [$userid-eq 0]; then

Echo "root"

Elif [$userid-ge 1000]; then

Echo "login user"

Else

Echo "system user"

Fi

2. Write scripts to achieve the following functions:

(1) list the following menus for users

Disk) show disks info (fdisk-l / dev/sda)

Mem) show memory info (free-m)

Cpu) show cpuinfo (using cat / proc/cpuinfo or lscpu)

*) quit

(2) prompt the user to give his or her choice, and then display the corresponding system information corresponding to his or her choice

Cat / dev/null;then

Echo "$username exists"

Esle

Useradd $username & & echo "add user $username finished"

Fi

Done

For example: create 10 files F1-10 under the tmp directory

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

Touch / tmp/f$filename

Done

Note: when, we should consider the judgment condition; as in the above example, we should first judge whether the file exists.

For example: find the sum of all positive integers within 100

Declare-I sum=0

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

Sum=$ [$sum+$i]

Done

Echo $sum

For example: calculate the odd number and the sum of 100

Declare-I sum=0

For i in $(seq 1 2 100); do

Sum=$ [$sum+$i]

Done

Echo $sum

For example: calculate the even number and sum within 100

Declare-I sum=0

For i in $(seq 2 2 100); do

Sum=$ [$sum+$i]

Done

Echo $sum

Example: determine the type of each file in the / var/log directory

File / var/log/* can be judged, but it is required to be implemented in a loop.

For filename in / var/log/*;do

If [- f $filename]; then

Echo "this is common file"

Elif [- d $filename]; then

Echo "this is directory file"

Elif [- L $filename]; then

Echo "this is softlink"

Elif [- b $filename]; then

Echo "this is block file"

Elif [- c $filename]; then

Echo "this is character file"

Elif [- S $filename]; then

Echo "this is socket file"

Elif [- p $filename]; then

Echo "thisi is pipe file"

Else

Echo "unknow file type"

Fi

Done

Exercise:

1. Find the sum of even numbers and odd numbers within 100 respectively

Calculate the odd number and sum within 100

Declare-I sum=0

For i in $(seq 1 2 100); do

Sum=$ [$sum+$i]

Done

Echo $sum

Calculate the sum of even numbers within 100

Declare-I sum=0

For i in $(seq 2 2 100); do

Sum=$ [$sum+$i]

Done

Echo $sum

2. Calculate the sum of the id of all users on the current system

Declare-I sum=0

For i in $(cut-d:-f3 / etc/passwd); do

Echo "\ $sum=$sum,\ $iSuppli"

Sum=$ [$sum+$i]

Done

Echo $sum

3. Pass a directory to the script through the script parameters, and then calculate the sum of the lines of all text files in this directory; and indicate the total number of such files

! [$#-eq 1] & & exit 1

! [- d $1] & & echo "please give a comment file" & & exit 2

Declare-I filesum=0

Declare-I sum=0

Declare-I Arom0

For i in $(ls $1); do

If [- f $I]; then

Cut $(wc-l $I | cut-d ""-F1)

Aphrodite 1

Sum=$ [$sum+$a]

Echo "file line sum=$a,files sum $A Magi all file line sum is $sum"

Else

Echo "this file not text type"

Fi

Done

For circular format:

For VARAIBLE in LIST;do

Cyclic body

Done

There are many ways to generate a LIST list: any command that can return a list, such as {#.. #} or glob (/ tpm/test/*), can be given directly.

Special uses of for loops:

For ((control variable initialization; conditional judgment expression; modified statement of control variable); do

Cyclic body

Done

Note: conditional judgment can be used directly.

Control variable initialization: executed only once when the loop code starts to run

Control variable correction statement: the control variable correction operation will be carried out at the end of each cycle, and then the condition judgment will be made.

Example: find the sum of integral positive numbers within 100

Declare-I sum=0

For ((item1witi > / tmp/users.log

Or rewrite it as:

Until who | grep "^ aaa\ >" & > / dev/null;do

Sleep 3

Done

Echo "$(date +" F% T ") aaa longed on" > > / tmp/user.log

Special use of the while loop (traversing the lines of the file):

While read VARIABLE;do

Cyclic body

Done

< /PATH/FROM/SOMEFILE 依次读取/PATH/FROM/SOMEFILE文件中的每一行，且将其值赋值给VARIABLE变量； 示例：找出ID号为偶数的用户，显示器用户名、ID及默认shell； while read line;do userid=$(echo $line |cut -d: -f3) username=$(echo $line |cut -d: -f1) usershell=$(echo $line |cut -d: -f7) if [ $[$userid%2] -eq 0 ];then echo "$username,$userid,$usershell" fi done < /etc/passwd bash脚本编程之用户交互 脚本参数 用户交互：通过键盘输入数据 read [OPTION] ... [name ...] -p 'PROMPT'：输出提示符，设置提示信息；； -t TIMEOUT：设定超时退出时间； name：是在脚本里设定的变量； bash -n /path/to/some_script 检测脚本中的语法错误 bash -x /path/to/some_script 调试执行 例如：脚本实现，使用read添加用户，密码同用户名； read -p "plase give a username and passwd: " a b useradd $a echo $a echo $b echo "$b "| passwd $a --stdin &>

/ dev/null

For example: script interaction, enter a specified user name, create a user and set a password

Read-p "Enter a username:" name

[- z "$name"] & & ehco "a username is needed" & & exit 2

Read-p "enter a passwd for $name, [passwd]:" passwd

[- z "$passwd"] & & passwd= "passwd"

If id $name & > / dev/null;then

Echo "$name exists"

Else

Useradd $name

Echo "$passwd" | passwd-- stdin $name & > / dev/null

Echo "add user $name finished"

Fi

Exercise:

1. Judge who is big and who is small when given two values.

A method of giving a numerical value; command parameters, command interaction

Read-p "give two number:" a b

! [$#-eq 2] & & echo "give two number" & & exit 1

If [$a-gt $b]; then

Echo "$an is bigger"

Else

Echo "$b is bigger"

Fi

2. Prompt the user to enter a string. If the input is quit, exit, otherwise the string content will be displayed.

Read-p "give a string:" a

If! [$a = = quit]; then

Echo "show string is $a"

Else

Exit 1

Fi

Background: new employees of the company should open system accounts and count out the information of new employees (through interaction)

Let the user specify a user name and password. If the user name exists before, delete it first, and then add the system account for the user.

After completion, you need to count the employee's mobile phone number, email,qq, age, and store them in the user's home directory after collection.

When the above is done, ask the user if he or she needs to create a separate working directory for the user as / data/username. The default is to do so. If not, enter n or N

Read-p "input a password for useradd:" password

Echo $password | passwd-- stdin $username & > / dev/null

Echo "user's password is add finished"

Read-p "input personal infomation:tel):" tel

Echo "$username tel:$tel" > > / home/$username/userinfo.txt

Read-p "input personal infomation:email):" email

Echo "$username email:$email" > > / home/$username/userinfo.txt

Read-p "input personal infomation:qq):" qq

Echo "$username qq:$qq" > > / home/$username/userinfo.txt

Read-p "input personal infomation:age):" age

Echo "$username age:$age" > > / home/$username/userinfo.txt

Read-p "you if create personal work DIR (ymp nrecom N) default: y:" dir

If ["$dir" = = "y"]; then

Mkdir-p / data/$username

Elif ["$dir" = = "n"-o "$dir" = = "N"]; then

Echo "you choice nocreate personal work DIR,bye"

Exit 2

Fi

Conditional selection of case statements for bash script programming

Case statement:

Multi-branch in statements in if:

If CONDITION1;then

Branch 1 (statement executed when CONDITION1 is true)

Elif CONDITION2;then

Branch 2 (statement executed when CONDITION2 is true)

...

Else CONDITION;then

Branch n

Fi

Example: display a menu to the user

Disk) show disk info

Mem) show memory info

Cpu) show cpu info

*) QUIT

Requirements: (1) prompt users to give their own choices

(2) the correct selection gives the corresponding information, otherwise, it is prompted to re-select the correct option.

Cat / dev/null;then

Grep "^ $username\ >" / etc/passwd | cut-d:-f3mem7

Else

Echo "no such user"

Fi

}

Username=$1

Userinfo

Username=$2

Userinfo

Example: rewrite script service framework (service scripts cannot end in .sh)

# chkconfig:-50 50

# description: test service script

#

Prog=$ (basename $0)

Lockfile=/var/lock/subsys/$prog

Start () {

If [- f $lockfile]; then

Echo "$prog is running yet"

Else

Touch $lockfile

Lockfile=/var/lock/subsys/$prog

Start () {

If [- f $lockfile]; then

Echo "$prog is running yet"

Else

Touch $lockfile

[$?-eq 0] & & echo "start $prog finished"

Fi

}

Stop () {

If [$lockfile]; then

Rm-f $lockfile

[$?-eq 0] & & echo "stop $prog finished"

Else

Echo "$prog is not running"

Fi

}

Restart () {

If [- f $lockfile]; then

Rm-f $lcokfile

Touch $lockfile

Echo "restart $prog finished"

Else

Touch-f $lockfile

Echo "start $prog finished"

Fi

}

Status () {

If [- e $lockfile]; then

Echo "$prog is running"

Else

Echo "$prog is stopped"

Fi

}

Usage () {

Echo "Usage: $prog {start | stop | restart | status}"

Exit 1

}

Case $1 in

Start)

Start

Stop)

Stop

Restart)

Stop

Start

Status)

Suatus

*)

Usage

Exit 1

Esac

The return value of the function:

The value returned from the execution result of the function:

(1) use the echo or printf command for output

(2) the execution result of the command called in the function body

Exit status code of the function:

(1) default depends on the exit status code of the last command executed in the function body

(2) Custom: use return #

There are two kinds of return values for commands, one is the return value for the execution result, and the other is the exit status code; when the command replacement is implemented in the script, the result of command execution is called at the place of command replacement, and so is the function. Function substitution is the place where the function is called, that is, the result of function code execution; printf command: no line wrapping is allowed, but the output can be defined as formatted output. It will be introduced in the awk command

The function can accept parameters:

Pass parameters to the function:

In the function body, you can use $1, $2,. Reference the parameters passed to the function; you can also use $* or $@ to refer to all parameters in the function, and $# to refer to the number of parameters passed

When calling a function, the given argument list is separated by a space character after the function name, for example, testfunction arg1 agr2 agr3...

Example: add 10 users, use the function implementation, and pass the user name as an argument to the function

] # bash-x exercise.sh aaa

Addusers () {

If id $1 & > / dev/null;then

Return 5

Else

Useradd $1

Retval=$?

Return $retval

Fi

}

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

Addusers ${1} ${I}

Retval=$?

If [$retval-eq 0]; then

Echo "add user ${1} ${I} finished"

Elif [$retval-eq 5]; then

Echo "user ${1} ${I} exist"

Else

Echo "unkown error"

Fi

Done

Exercise:

1. The script function implements the ping host to test the host's online status.

Main program: to test the online status of hosts in the range of 172.16.1.1-172.16.67.1

Implemented using for,while and until loops, respectively

Common way:

Declare-I uphosts=0

Declare-I downhosts=0

For i in {1... 67}; do

If ping-W 1-c 1 172.16.$i.1 & > / dev/null;then

Echo "172.16.$i.i is up"

Let uphosts+=1

Else

Echo "172.16.$i.1 is down"

Let downhosts+=1

Fi

Done

Echo "Up hosts: $uphosts,Down hosts: $downhosts"

Revision 2: function + while loop:

Declare-I uphosts=0

Declare-I downhosts=0

Declare-iionization 1

Hostping () {

If ping-W 1-c 1 $1 & > / dev/null;then

Echo "$i is up"

Let uphosts+=1

Else

Echo "$1 is down"

Let downhosts+=1

Fi

}

While [$I-le 67]; do

Hostping 172.16.$i.1

Let iTunes +

Done

Echo "Up hosts: $uphosts,Down hosts: $downhosts"

Revision 3: use return to count the number of hosts in ping in the main program

Declare-I uphosts=0

Declare-I downhosts=0

Declare-iionization 1

Hostping () {

If ping-W 1-c 1 $1 & > / dev/null;then

Echo "$i is up"

Return 0

Else

Echo "$1 is down"

Return 1

Fi

}

While [$I-le 67]; do

Hostping 172.16.$i.1

[$?-eq 0] & & let uphosts++ | | let downhosts++

Let iTunes +

Done

Echo "Up hosts: $uphosts,Down hosts: $downhosts"

2. Realize script function and print nn multiplication table.

Variable scope:

Local variable: the scope is the life cycle of the function; it is automatically destroyed at the end of the function

Method for defining local variables: local VARIABLE=VALE

Local variable: scope is the life cycle of the shell process that runs the script; therefore, its scope is the current shell script program file

For example:

Name=tom

Setname () {

Name=jerry

Echo "Function: $name"

}

Setnaem

Echo "Shell: $name"

In this case, the name of the function and the name of shell are both jerry, and the variable name is a local variable, which can be called in the function.

The display results are as follows:

Function:jerry

Shell: jerry

If it is changed to: local name=jerry in the above statement

The display results are as follows:

Function:jerry

Shell: tom

Function recursion for bash scripting:

Function calls itself directly or indirectly

Function recursion is used when doing factorial or Fibonacci series.

For example: 10! = 10: 9! = 10'9'8! = 10'9'8'7! ... = 10'9'8'7'6'5'4'3'2'1!

The factorial transfer parameter of the function is n

N * (nmur1)! = n* (nmel1) * (nmur2)! =.

For example: Fibonacci series

Each value is the sum of the first two numbers; a function is used to find out what the number of order n is.

1 1 2 3 5 8 13 21...

For example, the passing parameter is a number to realize the factorial of the number.

Fact () {

If [$1-eq 0-o $1-eq 1]; then

Echo 1

Else

Echo $[$1mm $(fact $[$1-1])]

Fi

}

Fact $1

For example: pass a parameter to a number to implement the Fibonacci sequence

Fab () {

If [$1-eq 1]; then

Echo-n "1"

Elif [$1-eq 2]; then

Echo-n "1"

Else

Echo-n "$[(fab $[$1-1]) + $(fab $[$1-2])]"

Fi

}

For i in $(seq 1 $1); do

Fab $I

Done

Ech

An array of bash script programming

Functions, case statements

Case statement syntax format:

Case $VARIABLE in

PAT1)

Branch 1

PAT2)

Branch 2

...

*)

Branch n

Esac

PATTERN: is a Glob wildcard

Function: can complete structured programming and realize code reuse

Function function_name {

Function body

}

Function_name () {

Function body

}

After the function is defined, the called function can be executed.

Function call: you can call a given function name, or you can pass parameters to the function, using the position parameter $1.

Local variable: local VARIABLE

When the life cycle is to call a function, the body of the function

Array:

Program = instruction + data

Instructions in bash scripts: syntax keywords in the whole programming, plus commands on various systems, plus defined functions

Data: exists in variables, files, or data organization structures

Variables: memory space that stores a single element

Array: contiguous memory space for storing multiple elements

Array name: the entire array has only one name; the number stored in the first memory space of the array is the location where the array name points.

Array index: the number starts at 0; the data method of referencing the array species:

Array name [index]

${ARRAY_ name [index]}

Note: bash-4 and later versions support custom indexing format, not just 0meme 1pm 2pm. Digital format

A generic group in a custom index format, called an associative array

Declare an array:

Declare-a NAME: declare an indexed array

Declare-A NAME: declare an associative array

View the statement help:

] # help declare

The data in the array is a continuous memory space that exists in memory, storing multiple consecutive data separately, each data is an independent managed unit, but there is no independent name, it should be indexed by the array name, and the array name plus a subscript can be understood as the identifier of the data in the array.

How the elements in the array are assigned:

(1) assign only one element at a time:

ARRAY_ name [index] = value

For example:

] # animals [0] = pig

] # animals [1] = cat

] # echo $animals

] # echo ${animals [1]}

(2) assign all elements at once:

ARRAY_NAME= ("VAL1", "VAL2", "VAL3"...)

Will automatically assign a value of 0, 1, 2, 3, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,

For example:

] # weekdays= ("Monday"Tuseday"Wednesday")

] # echo ${weekdays [2]}

(3) only specific elements are assigned

ARRAY_NAME= ([0] = "VAL1" [3] = "VAL4"...)

An array in a sparse format

Note: bash supports arrays in sparse format

For example:

] # sword= ([0] = "Yitian" [3] = "Tulong")

] # echo ${sword [1]}: displayed as empty

] # echo ${sword [3]}: displayed as Tulong

(4) read-an ARRAY_NAME

For example:

] # read-a Linux

Sed awk find grep

] # echo ${Linux [1]}: displayed as awk

Associative array:

] # declare-A world: declare an associative array

] # world [us] "America"

] # echo "${world [us]}": displayed as America

] # world [uk] "unite kingdom"

] # echo "${world [uk]}": displayed as unite kingdom

Reference elements in the array: ${ARRAY_ name [index]}

Note: when referencing, only the array name is given, which indicates that the element with subscript 0 is referenced

${ARRAY_NAME [*]}: references all elements in the array

${ARRAY_NAME [@]}: ditto

Length of the array (number of elements in the array):

${# ARRAY_NAME [*]}

${# ARRAY_NAME [@]}

For example:

] # echo "${# Linux [*]}: displays the number of array elements 4

] # echo "${# animals [@]}: displays the number of array elements 2

] # echo "${# animals}: displays 3 characters for the first element of the array

] # echo "${animals [*]}: displays all elements in the array; generates a list

Example: generate 10 random numbers and find out the maximum and minimum values

Declare-a rand

Declare-I max=0

For i in {0.. 9}; do

Rand [$I] = $RANDOM

Echo ${rand [$I]}

[${rand [$I]}-gt $max] & & max=$ {rand [$I]}

Done

Echo "Max: $max"

Exercise:

1. Generate 10 random numbers, from small to sorted

2. Define an array whose elements are all files ending in .log in the / var/log directory; count the sum of lines in files whose subscript is even

Declare-a files

Files= (/ var/log/*.log)

Declare-I lines=0

For i in $(seq 0 $[${# files [*]}-1]); do

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

Let lines+=$ (wc-l ${files [$I]} | cut-d'- F1)

Fi

Done

Echo "lines: $lines"

Reference all elements in the array:

${ARRAY_NAME [*]}

${ARRAY_NAME [@]}

You can also return only a limited number of elements

Array element slicing: ${ARRAY_NAME [@]: offset:number}

Offset: element offset

Number: take the number of elements; when number is omitted, all elements after the offset are taken

For example:

] # files= (/ etc/ [Pp] *)

] # echo ${files [*]}

Display the results:

/ etc/pam.d / etc/passwd / etc/passwd- / etc/pinforc / etc/pkcs11 / etc/pki / etc/plymouth / etc/pm / etc/polkit-1 / etc/popt.d / etc/postfix / etc/ppp / etc/prelink.conf.d / etc/printcap / etc/profile / etc/profile.d / etc/protocols / etc/pulse

] # echo ${files [@]: 2:3}: skips 2 from the above array and takes 3

Display the results:

/ etc/passwd- / etc/pinforc / etc/pkcs11

] # echo ${files [@]: 5}

Display the results:

/ etc/pki / etc/plymouth / etc/pm / etc/polkit-1 / etc/popt.d / etc/postfix / etc/ppp / etc/prelink.conf.d / etc/printcap / etc/profile / etc/profile.d / etc/protocols / etc/pulse

Append elements to an array in a non-sparse format:

ARRAY_NAME [${# ARRAY_NAME [*]}] =

${# ARRAY_NAME [*]}]: indicates the number of elements in the fetched array

Delete an element from the array:

Unset ARRAY [INDEX]

Associative array:

Declare-An ARRAY_NAME

ARRAY_NAME= ([index_name1] = "value1" [index_name2] = "value2"...)

Bash's built-in string processing tool for bash scripting:

String slicing: (string based on location)

${var:offset:number}: take a substring of a string

${var:-length}: take the rightmost characters of the string

Note: there must be a space after the colon

For example:

] # name=jerry

] # echo ${name:2}

Display result: rry

] # echo ${name:2:2}

Display result: rr

] # echo ${name:-4}

Display result: erry

Take the string based on the pattern:

${var#*word}:

Where word is a read-only delimiter; function: from left to right, find the first occurrence of the word delimiter in the string stored by the var variable, and delete all characters between the beginning of the string and the delimiter

${var##*word}: (can be used to get the path base name and port number)

Where word is a read-only delimiter; function: from left to right, find the last word delimiter in the string stored by the var variable, and delete all characters between the beginning of the string and the delimiter

For example:

] # mypath= "/ etc/init.d/functions"

] # echo ${mypath#*/}: display content: etc/init.d/functions

] # echo ${mypath##*/}: display content: functions; (take the base name of the path)

${var%word*}: (can be used to get a path name)

Where word is a read-only delimiter; function: from right to left, find the word delimiter that appears for the first time in the string stored by the var variable, and delete all characters from the delimiter to the end of the string

${var%word*}:

Where word is a read-only delimiter; function: from right to left, find the last word delimiter in the string stored by the var variable, and delete all characters from the delimiter to the end of the string

For example:

] # echo ${mypath%/*}: display content: / etc/init.d; (that is, the path name)

] # echo ${mypath%%/*}: display content: empty

] # mypath= "etc/init.d/functions"

] # echo ${mypath%%/*}: display content: etc

] # url= "http://www.magedu.com:80"

] # echo ${url##*:}: display content: 80; (take port number)

] # echo ${url%%:*}: display content: http

Find and replace:

${var/PATTERN/SUBSTI}:

Find the string represented by var that is matched by PATTERN for the first time and replace it with the string represented by SUBSTI

${var//PATTERN/SUBSTI}:

Find all the strings matched by PATTERN in the string represented by var and replace them all with the string represented by SUBSTI

Anchor at the beginning / end of the line:

${var/#PATTERN/SUBSTI}:

Find the string represented by var to which the beginning of the line is matched by PATTERN and replace it with the string represented by SUBSTI

${var/%PATTERN/SUBSTI}:

Find the string represented by var to which the end of the line is matched by PATTERN and replace it with the string represented by SUBSTI

Note: use glob-style wildcards in PATTERN

For example:

] # userinfo= "root:x:0:0:root admin:/root:/binb/chroot"

] # echo ${userinfo/root/ROOT}: display: ROOT:x:0:0:root admin:/root:/binb/chroot; replacement for the first time

] # echo ${userinfo//r??t/ROOT}: display content: ROOT:x:0:0:ROOT admin:/ROOT:/binb/chROOT; replaces all

] # echo ${userinfo/#r??t/ROOT}: display content: ROOT:x:0:0:root admin:/root:/binb/chroot; line header replacement

] # echo ${userinfo/%r??t/ROOT}: display content: root:x:0:0:root admin:/root:/binb/chROOT; end-of-line replacement

Find and delete:

${var/PATTERN}: find the var string and delete only the string that was matched by PATTERN for the first time

${var//PATTERN}: find the var string and delete all strings matched by PATTERN

${var/#PATTERN}: find the string represented by var and delete only the string to which the beginning of the line is matched by PATTERN

${var/%PATTERN}: find the string represented by var and delete only the string to which the end of the line is matched by PATTERN

Character case conversion:

${var^ ^}: converts all lowercase characters in var to uppercase characters

${var,}: converts all uppercase characters in var to lowercase characters

For example:

] # url= "http://www.magedu.com:80"

] # echo ${URL ^ ^}: display content: HTTP://WWW.MAGEDU.COM:80; to uppercase:

] # myurl=$ {URL ^ ^}

] # echo ${myurl,}: display content: http://www.magedu.com:80; converted to lowercase

Variable assignment:

${var:-VALUE}: returns VALUE if the var variable is empty or is not set, otherwise, returns the value of the var variable

${var:=VALUE}: if the var variable is empty or not set, return VALUE and assign VALUE to the var variable, otherwise, return the value of the var variable

For example:

The variable hi is empty and has no defined value

] # echo ${hi:-world}: display content: world

] # hi= "hello"

] # echo ${hi:-world}: display content: hello

] # echo ${hi:=world}: display content: hello

] # unset hi: undo the value of the hi variable

] # echo ${hi:=world}: display content: world

] # echo $hi: the hi variable is assigned at this time

${var:+VALUE}: if the var variable is not empty, return VALUE;. Otherwise, it doesn't make sense.

${var:?ERRO_INFO}: if the var variable is empty or is not set, return ERRO_INFO as an error prompt; otherwise, return the value of var

Exercise: the script completes the following functions; (it must be completed, which will be used in subsequent course experiments)

(1) prompt the user for the name of an executable command

(2) get the list of all library files that this command depends on

(3) copy the command to the corresponding path under a directory (for example, / mnt/sysroot, that is, take this directory as the root)

Bahs,/bin/bash = > / mnt/sysroot/bin/bash

Usradd,/usr/sbin/useradd = > / mnt/sysroot/usr/sbin/usradd

(4) copy all the library files that this command depends on to the corresponding path under the directory.

/ lib64/ld-linux-x8664.so2 = > / mnt/sysroot/lib64/ld-linux-x8664.so.2

Further:

After each copy completes one command, do not quit, but prompt the user to continue to enter other commands to copy, and repeat the above function until the user enters "quit" to exit the script

Write a script: answer to the previous exercise

Use the ping command to detect whether all hosts in the range of 172.16.1.1-172.16.67.1 are online, online as up, and not online as down, and count the number of hosts respectively.

Implemented using for,while and until loops, respectively

Common way:

Declare-I uphosts=0

Declare-I downhosts=0

For i in {1... 67}; do

If ping-W 1-c 1 172.16.$i.1 & > / dev/null;then

Echo "172.16.$i.i is up"

Let uphosts+=1

Else

Echo "172.16.$i.1 is down"

Let downhosts+=1

Fi

Done

Echo "Up hosts: $uphosts,Down hosts: $downhosts"

Revision 2: function + while loop:

Declare-I uphosts=0

Declare-I downhosts=0

Declare-iionization 1

Hostping () {

If ping-W 1-c 1 $1 & > / dev/null;then

Echo "$i is up"

Let uphosts+=1

Else

Echo "$1 is down"

Let downhosts+=1

Fi

}

While [$I-le 67]; do

Hostping 172.16.$i.1

Let iTunes +

Done

Echo "Up hosts: $uphosts,Down hosts: $downhosts"

Revision 3: use return to count the number of hosts in ping in the main program

Declare-I uphosts=0

Declare-I downhosts=0

Declare-iionization 1

Hostping () {

If ping-W 1-c 1 $1 & > / dev/null;then

Echo "$i is up"

Return 0

Else

Echo "$1 is down"

Return 1

Fi

}

While [$I-le 67]; do

Hostping 172.16.$i.1

[$?-eq 0] & & let uphosts++ | | let downhosts++

Let iTunes +

Done

Echo "Up hosts: $uphosts,Down hosts: $downhosts"

Exercise: script implementation to detect whether all hosts in Class C, Class B, and Class A networks are online

Cping () {

Local iTunes 1

While [$I-le 245]; do

If ping-W 1-c 1 $1.Secreti & > / dev/null;then

Echo "$1.Secreti is up"

Else

Echo "$1.Secreti is down"

Fi

Let iTunes +

Done

}

# cping 192.168.0

Bping () {

Local jung0

While [$j-le 255]; do

Cping $1.10j

Let jacks +

Done

}

# bping 172.16

Aping () {

Local Xero0

While [$x-le 255]; do

Bping $1.0x

Let Xerox +

Done

}

Aping 10

Extension: the above script can be modified to prompt users to enter any network address or network address, get their network, and scan their network segments

All can ping this address, first determine the ip address category, and then call the corresponding function. For example, if the input is 10.0.0.1, cut out the first paragraph of the ip address to compare whether it is A (127,128191,192223), and then call the corresponding function implementation within their respective scope.

Signal capture of bash script programming

Trap command: just open the net to capture the signal on the first line of the script

Trap 'COMMAND' SIGANLS

-l: list signals

You can often capture signals: HUP, INT

COMMAND: you can use semicolons to separate multiple commands, or it can be a function

Note: the trap command cannot capture signals: 15-SIGTERM (terminal) and 9-SIGKILL (kill).

Because the main purpose of capturing a signal is to define what to do once the signal arrives, it may not be the default operation, so kill signals and other signals cannot be captured at will.

View the list of signals:

] # trap-l

] # kill-l

Check the signal type explanation:

] # man 7 signal

For example:

Trap 'echo "quit"; exit 1' INT

For i in {1... 254}; do

Ping 172.16.$i.1

Done

Example: using trp capture, function implementation

Ping172.16.1-254.1 saves the results in the temporary directory created under the / tmp/ directory, and then deletes those temporary files when you exit

This script cannot delete temporary files that were not captured last time.

Declare-a hosttmpfiles

Trap' mytrap' INT

Mytrap () {

Echo "quit"

Rm-f ${hosttmpfiles [@]}

Exit 1

}

For i in {1... 50}; do

Tmpfile=$ (mktemp / tmp/ping.XXXXX)

If ping-W 1-c 1 172.16.$i.1 & > / dev/null;then

Echo "172.16.$i.1 is UP" | tee $tmpfile

Else

Echo "172.16.$i.1 is down" | tee $tmpfile

Fi

Hosttmpfiles [${# hosttmpfiles [*]}] = $tmpfile

Done

Use ACSII colors in bash:

Format:\ 033 [front # landscape # color; back # landscape # color mSTRING\ 033 [0m]

\ 033 [#; # # mSTRING\ 033 [0m

Multiple controllers can be combined and separated by semicolons

\ 033 [31mhello\ 033 [0m

\ 033 [: indicates the control key Ctrl

\ 033 [0m: indicates the end of control

31m: represents the foreground color

Left digit: (foreground and background color can be set at the same time)

3: indicates the foreground color

4: represents the background color

Number on the right: indicates color

1: red

2: green

3: gold

4: blue

5: purple

6: cyan

7: Gray

For example:\ 033 [3mhello\ 033 [0m]

# m: indicates the font

1: bold

4: underline

5: flashing

7: front background reverse color

8: hidden

For example:

] # echo-e "\ 033 [31mhello\ 033 [0m": the foreground color is red

] # echo-e "\ 033 [41mhello\ 033 [0m": the background color is red

] # echo-e "\ 033 [41 × 32mhello\ 033 [0m": green foreground and red background

] # echo-e "\ 033 [7mhello\ 033 [0m": front background inverted

] # echo-e "\ 033 [4mhello\ 033 [0m": underlined

] # echo-e "\ 033 [42transfer35ter5mhello\ 033 [0m": green background, purple foreground, flickering

Built-in environment variable: PS1

Command line prompt format

The command line prompt format can be customized:

Export PS1=' [\ 033 [31m\ u\ 033 [0m @\ 033 [32m\ h\ 033 [0m\ 033 [35m\ W\ 033 [0m]\ $'

But after setting, there are side effects.

For example:

] # echo $PS1

Display content: [\ u@\ h\ W]\ $

Dialog command: (requires yum install installation)

Display dialog boxes from shell scripts

Dialog common-options box-options

Box-options:

There are three parameters: text, height, and width

-- calendar: calendar box

-- dselect: select the catalog box

-- editbox: edit box

-- form: form

-- gauge: progress bar

-- infobox: information box

-- inputbox: enter null

-- inputmenu: enter menu

-- menu: menu

-- msgbox: message box

-- passwordbox: password box, displayed as *

] # yum info dialog: check whether the dialog command has an installation package available

] # yum install dialog: install the dialog package

For example:

] # dialog-- msgbox hell 17 30: output message box 17 high and 30 wide

The dialog command enables windowing programming; some are implemented by calling curses in the C library.

Research:

Dialog command, how to use each form control

How do I get what the user selects or types? The default output of the dialog command is directed to the error output stream

Dialog $(dialog), the result should be saved in the variable, but cannot be assigned to the variable. You need to apply the option-- stdout in the variable command.

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