Shell

Shell It's a command line interpreter , It accepts application and user commands , And then invoke the kernel of the operating system .

Linux Provided Shell Parser has

[bd@localServer ~]$ cat /etc/shells 
/bin/sh
/bin/bash
/sbin/nologin
/bin/dash
/bin/tcsh
/bin/csh

bash and sh The relationship between , call sh What is actually called is bash, They are soft connections

Centos The default parser is bash

[bd@localServer ~]$ echo $SHELL
/bin/bash

Shell introduction

Script format ： Script to #!/bin/bash start （ Specify the parser ）

Common execution methods of scripts （ With /home/test.sh For example ）

The first one is ： use bash or sh+ Relative or absolute path of script （ Don't assign script +x jurisdiction ）

sh+ Relative path of script 
sh test.sh

sh+ The absolute path of the script 
sh /home/test.sh

bash+ Relative path of script 
bash test.sh

bash+ The absolute path of the script 
bash /home/test.sh

The second kind ： Execute the script using the absolute or relative path of the input script （ Must have executable permissions +x）

#  Relative paths 
[bd@localServer ~]$ ./test.sh

#  Absolute path 
[bd@localServer ~]$ /home/test.sh

Be careful ： First execution method , The essence is bash Parsers help you execute scripts , So the script itself does not need execution permission . The second method of execution , The essence is that scripts need to be executed by themselves , Therefore, execution permission is required .

Shell The variables in the

System variables

Common system variables

$HOME、$PWD、$SHELL、$USER etc.

##  View the value of the system variable 
[bd@localServer ~]$ echo $HOME
/home/bd

##  Show the current Shell All variables in ：set
[bd@localServer ~]$ set
BASH=/bin/bash
BASH_ALIASES=()
BASH_ARGC=()
BASH_ARGV=()
...

Custom variable

Basic grammar

​ （1） Defining variables ： Variable = value

​ （2） Revoke variables ：unset Variable

​ （3） Declare static variables ：readonly Variable , Be careful ： You can't unset

Variable definition rules

​ （1） Variable names can be alphabetized 、 Numbers and underscores , But it can't start with a number , Environment variable name is recommended to be capitalized .

​ （2） No spaces on both sides of equal sign

​ （3） stay bash in , Variable default type is string type , No direct numerical operation .

​ （4） Value of variable if there is a space , Double or single quotes are required .

Case practice

##  Defining variables A
[bd@localServer ~]$ A=5
[bd@localServer ~]$ echo $A
5

##  To the variable A Reassign 
[bd@localServer ~]$ A=8
[bd@localServer ~]$ echo $A
8

##  Revoke variables A
[bd@localServer ~]$ unset A
[bd@localServer ~]$ echo $A


##  Declare static variables B=2, You can't unset
[bd@localServer ~]$ readonly B=2
[bd@localServer ~]$ echo $B
2

[bd@localServer ~]$ B=9
-bash: B: readonly variable

##  stay bash in , Variable default type is string type , No direct numerical operation 
[bd@localServer ~]$ C=1+2
[bd@localServer ~]$ echo $C
1+2

##  Value of variable if there is a space , Double or single quotes are required 
[bd@localServer ~]$ D=I love sanguo
-bash: world: command not found

[bd@localServer ~]$ D="I love sanguo"
[bd@localServer ~]$ echo $A
I love sanguo

##  Variable can be promoted to global environment variable , For other purposes Shell Program usage 
export  Variable name 

[bd@localServer ~]$ vim test.sh 

test.sh Add to file echo $B

#!/bin/bash

echo "helloworld"
echo $B


[bd@localServer ~]$ ./helloworld.sh 
Helloworld

 Found no printout variables B Value .

[bd@localServer ~]$ export B
[bd@localServer ~]$ ./helloworld.sh 
helloworld
2

Special variables ：$n

Basic grammar

$n

Function description ：n Is the number ,$0 Represents the script name ,$1-$9generationsurfaceThe\; firstOneToThe\; firstNineindividualginsengCount,TenWithOnOfginsengCountNeed\; to\; bewantuseBigenclosedNumberpackagecontain,Such\; as${10}

Case practice

##  Output the script file name 、 Input parameters 1 And input parameters 2  Value 
[bd@localServer ~]$ touch parameter.sh 
[bd@localServer ~]$ vim parameter.sh

#!/bin/bash

echo "$0  $1   $2"

[bd@localServer ~]$ chmod 777 parameter.sh

[bd@localServer ~]$ ./parameter.sh cls  xz
./parameter.sh  cls   xz

Special variables ：$#

Basic grammar

$#

Function description ： Get the number of all input parameters , Commonly used in cycles

Case practice

##  Get the number of input parameters 
[bd@localServer ~]$ vim parameter.sh

#!/bin/bash

echo "$0  $1   $2"
echo $#

[bd@localServer ~]$ chmod 777 parameter.sh
[bd@localServer ~]$ ./parameter.sh cls  xz
parameter.sh cls xz 
2

Special variables ：KaTeX parse error: Undefined control sequence: \* at position 1: \̲*̲、@

Basic grammar

$*

Function description ： This variable represents all the parameters on the command line ,$* Treat all parameters as a whole

$@

Function description ： This variable also represents all the parameters on the command line , however $@ Treat each parameter differently

Case practice

##  Print all parameters entered 

[bd@localServer ~]$ vim parameter.sh
#!/bin/bash

echo "$0  $1   $2"
echo $#
echo $*
echo $@

 

[bd@localServer ~]$ bash parameter.sh 1 2 3
parameter.sh  1   2
3
1 2 3
1 2 3

Special variables ：$？

Basic grammar

$？

Function description ： Return status of last executed command . If the value of this variable is 0, Prove that the last command was executed correctly ; If the value of this variable is not 0（ Which number is it , It's up to the order itself ）, The last command was executed incorrectly .

Case practice

##  Judge helloworld.sh Whether the script is executed correctly 
[bd@localServer ~]$ ./helloworld.sh 
hello world

[bd@localServer ~]$ echo $?
0

Operator

Basic grammar

（1）“$((shipmentcounttype))”or“$[ Arithmetic expression ]”

（2）expr + , - , \*, /, % Add , reduce , ride ( stay expr Must be used later \*, stay $[shipmentcounttype]and$(( Arithmetic expression )), except , Remainder

Be careful ：expr Space between operators

Case practice ：

##  Calculation 3+2 Value 
[bd@localServer ~]$ expr 2 + 3
5

##  Calculation 3-2 Value 
[bd@localServer ~]$ expr 3 - 2 
1

##  Calculation （2+3）X4 Value 
### （a）expr One step calculation 
[bd@localServer ~]$ expr `expr 2 + 3` \* 4
20

###（b） use $[ Arithmetic expression ] The way 
[bd@localServer ~]$ S=$[(2+3)*4]
[bd@localServer ~]$ echo $S
20

conditional

Basic grammar

[ condition ]（ Be careful condition Space before and after ）

Be careful ： If the condition is not empty, it is true,[ test ] return true,[] return false.

Common judgment conditions

Compare two integers

= String comparison

-lt Less than （less than） -le Less than or equal to （less equal）

-eq be equal to （equal） -gt Greater than （greater than）

-ge Greater than or equal to （greater equal） -ne It's not equal to （Not equal）

Judge according to the file authority

-r Have read permission （read） -w Have the right to write （write）

-x Have the authority to execute （execute）

Judge according to the document type

-f The file exists and is a regular file （file）

-e File exists （existence）

-d The file exists and is a directory （directory）

Case practice

## 23 Greater than or equal to 22
[bd@localServer ~]$ [ 23 -ge 22 ]
[bd@localServer ~]$  echo $?
0

## test.sh Whether you have write permission 
[bd@localServer ~]$ [ -w helloworld.sh ]
[bd@localServer ~]$ echo $?
0

## /home/bd/cls.txt Does the file in the directory exist 
[bd@localServer ~]$ [ -e /home/bd/cls.txt ]
[bd@localServer ~]$ echo $?
1

##  Multi condition judgment （&&  Indicates that the previous command is executed successfully , To execute the last command ,||  Indicates that after the execution of the previous command fails , To execute the next command ）

[bd@localServer ~]$ [ condition ] && echo OK || echo notok
OK

[bd@localServer ~]$ [ condition ] && [ ] || echo notok
notok

Process control

if Judge

Basic grammar

if [  Conditional judgment  ];then 
   Program  
fi 

perhaps

if [  Conditional judgment  ] 
   then 
    Program 
fi

matters needing attention ：

（1）[ Conditional judgment ], There must be a space between the bracket and the conditional judgment

（2）if Space after

Case practice

##  Enter a number , If it is 1, The output this is 1, If it is 2, The output this is 2, If other , Output nothing .
[bd@localServer ~]$ touch if.sh
[bd@localServer ~]$ vim if.sh
#!/bin/bash

if [ $1 -eq "1" ]
	then
    echo "this is 1"
elif [ $1 -eq "2" ]
    then
    echo "this is 2"
fi

[bd@localServer ~]$ chmod 777 if.sh 
[bd@localServer ~]$ ./if.sh 1
this is 1

case sentence

Basic grammar

case $ Variable name  in 
    " value 1"） 
         If the value of the variable is equal to the value 1, Then execute the procedure 1 
        ;; 
    " value 2"） 
         If the value of the variable is equal to the value 2, Then execute the procedure 2 
        ;; 
    … Omit other branches … 
    *） 
         If none of the values of the variables are above , Then execute this procedure  
        ;; 
esac

matters needing attention ：

1. case Line ending must be a word “in”, Each pattern match must be in right parenthesis “）” end .

2. Double a semicolon “;;” Indicates the end of the command sequence , amount to java Medium break.

3. final “*）” Represents the default mode , amount to java Medium default.

Case practice

##  Enter a number , If it is 1, The output one, If it is 2, The output two, If other , Output other.

[bd@localServer ~]$ touch case.sh
[bd@localServer ~]$ vim case.sh

#!/bin/bash

case $1 in
    "1")
         echo "one"
         ;;
    "2")
         echo "two"
         ;;
    *)
         echo "other"
         ;;
esac


[bd@localServer ~]$ chmod 777 case.sh
[bd@localServer ~]$ ./case.sh 1
one

for loop

Basic grammar 1

for ((  Initial value ; Cycle control conditions ; Variable change  )) 
do 
     Program  
done

Case practice

##  from 1 Add to 100
[bd@localServer ~]$ touch for1.sh
[bd@localServer ~]$ vim for1.sh

#!/bin/bash

s=0
for((i=0;i<=100;i++))
do
    s=$[$s+$i]
done

echo $s


[bd@localServer ~]$ chmod 777 for1.sh 
[bd@localServer ~]$ ./for1.sh 
5050

Basic grammar 2

for  Variable  in  value 1  value 2  value 3… 
do 
     Program  
done

Case practice

## 1、 Print all input parameters 
[bd@localServer ~]$ touch for2.sh
[bd@localServer ~]$ vim for2.sh

#!/bin/bash
# Print digit 

for i in $*
do
    cho "this is $i"
done

[bd@localServer ~]$ chmod 777 for2.sh 
[bd@localServer ~]$ bash for2.sh 1 2 bd
this is 1
this is 2
this is bd

## 2、 Compare $* and $@ difference 
### 2.a、$* and $@ Represents all parameters passed to a function or script , Not double quoted “” Inclusion time , Are subject to $1 $2 …$n Output all parameters in the form of .
[bd@localServer ~]$ touch for.sh
[bd@localServer ~]$ vim for.sh

#!/bin/bash 
for i in $*
do
    echo "this is $i "
done

for j in $@
do      
    echo "that is $j"
done

[bd@localServer ~]$ bash for.sh 1 2 bd
this is 1 
this is 2 
this is bd 
that is 1
that is 2
that is bd

## 2.b、 When they are double quoted “” Inclusion time ,“$*” All parameters will be taken as a whole , With “$1 $2 …$n” Output all parameters in the form of ;“$@” Separate parameters , With “$1” “$2”…”$n” Output all parameters in the form of .
[bd@localServer ~]$ vim for.sh

#!/bin/bash 

#$* All parameters in are considered as a whole , So this for Loop only once  
for i in "$*" 
do 
    echo "this is $i"
done 

#$@ Each parameter in is considered independent , therefore “$@” There are several parameters in , It's going to cycle a couple of times  
for j in "$@" 
do 
    echo "that is $j" 
done

[bd@localServer ~]$ chmod 777 for.sh
[bd@localServer ~]$ bash for.sh 1 2 bd
this is 1 2 bd
that is 1
that is 2
that is bd

while loop

Basic grammar

while [  Conditional judgment  ] 
do 
     Program 
done

Case practice

##  from 1 Add to 100
[bd@localServer ~]$ touch while.sh
[bd@localServer ~]$ vim while.sh

#!/bin/bash

s=0
i=1

while [ $i -le 100 ]
do
    s=$[$s+$i]
    i=$[$i+1]
done

echo $s

[bd@localServer ~]$ chmod 777 while.sh 
[bd@localServer ~]$ ./while.sh 
5050

read Read console input

Basic grammar

read( Options )( Parameters )

 Options ：
	-p： Specify the prompt when reading the value ;
	-t： Specifies the time to wait while reading the value （ second ）, If you don't fill in, you will wait indefinitely 

 Parameters 
	 Variable ： Specifies the variable name of the read value 

​

Case practice

###  Tips 7 Seconds , Read the name entered by the console 
[bd@localServer ~]$ touch read.sh
[bd@localServer ~]$ vim read.sh

#!/bin/bash

read -t 7 -p "Enter your name in 7 seconds " NAME
echo $NAME

[bd@localServer ~]$ ./read.sh 
Enter your name in 7 seconds test
test

function

System function

basename

Basic grammar

##  Function description ：basename The command will delete all prefixes including the last （‘/’） character , Then display the string .
basename [string / pathname] [suffix]

##  Options ：
##    suffix For the suffix , If suffix Designated ,basename Will pathname or string Medium suffix Get rid of .

Case practice

##  Intercept this /home/bd/test.txt File name of the path 

[bd@localServer ~]$ basename /home/bd/test.txt 
test.txt

[bd@localServer ~]$ basename /home/bd/test.txt .txt
test

dirname

Basic grammar

##  Function description ： Remove filename from given filename with absolute path （ Non catalog part ）, Then return to the rest of the path （ Part of the catalog ）
dirname  File absolute path 

Case practice

##  obtain test.txt Path to file 
[bd@localServer ~]$ dirname /home/bd/test.txt 
/home/bd

Custom function

Basic grammar

##  All in brackets are optional , However, it is generally not omitted function And parentheses 
[ function ] funname[()]
{
    Action;
    [return int;]
}

funname

Experience and skill

（1） Must be before calling function place , Declare function first ,shell The script is run line by line . It doesn't compile first like any other language .

（2） Function return value , Only through $? System variable acquisition , Can display plus ：return return , If not , Results will be run with the last command , As return value .return Heel value n(0-255)

Case practice

##  Calculate the sum of the two input parameters 
[atguigu@hadoop101 datas]$ touch fun.sh
[atguigu@hadoop101 datas]$ vim fun.sh

#!/bin/bash

function sum()
{
    s=0
    s=$[ $1 + $2 ]
    echo "$s"
}

read -p "Please input the number1: " n1;
read -p "Please input the number2: " n2;
sum $n1 $n2;


[bd@localServer ~]$ chmod 777 fun.sh
[bd@localServer ~]$ ./fun.sh 
Please input the number1: 2
Please input the number2: 5
7