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Shell script Basics
2022-06-12 21:22:00 【mb61037a3723f67】
Catalog
- 2.1：shell Prompt （ understand ）：
- 2.2: shell Variable ：
- 2.3： shell Special variables ：
- 2.4： Replace ：
- 2.5： character string ：
- 2.6： Array ：
- 2.7： Operator ：
- 3.1： Enhanced Edition echo---printf
- 3.2: test command ：
- 3.3： Output , Input redirection
- Reference address ：http://c.biancheng.net/cpp/view/6995.html
One ：shell Basic grammar
1： The foundation of the script
- 1： shell Script naming conventions ： .sh ending .
- 2： shell The script must initially define the interpretation environment ： #!/usr/bin/bash
- 3: shell Script is not allowed to write Chinese .
- 4： Script description ： author , Creation time , edition , Script description .
#!/usr/bin/bash
#Author: liangShan
#Created Time:2021/08/30
#Release: 1.0
#Script Description: nginx install script
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- 5： Script composition ：
- Explain the environment ： #!/usr/bin/env
- annotated ：
- Execute code ：
- 6： Script run ：
- 1： Add execution permission ：
chmod +x Script name
./ Script
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- 2： The interpreter runs directly ：
bash Script - 7： shell Special symbols in ：
- 8： Common ones shell ：
- cat / etc/shells : see shell The order of ：
- The common one is ： sh, bash, dash
[email protected]:~$ cat /etc/shells
# /etc/shells: valid login shells
/bin/sh
/bin/bash
/usr/bin/bash
/bin/rbash
/usr/bin/rbash
/bin/dash
/usr/bin/dash
/usr/bin/tmux
/usr/bin/screen
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- View the default shell:
renshan[email protected]:~$ echo $SHELL
/bin/bash
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2: shell command ：
2.1：shell Prompt （ understand ）：
- shell The prompt format in is through ： PS1, and PS2 Two variables to null .
- for example ： The first one below is PS1 Format , The second is PS2 Format .
[email protected]:~$ echo "liangshan"
liangshan
[email protected]:~$ echo "
> liang
> shan
> "
liang
shan
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2.2: shell Variable ：
- shell There is only one type of variable in ： character string .
- Definition of variables ：
Variable name = value
Variable name =' value '
Variable name =" value "
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- 1： There must be no spaces on either side .
- 2： Variable name ： Numbers , Letter , Underline makes up , Letter , Start with an underline .
- Use of variables ： Recommended {}
${ Variable }
$ Variable
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- The difference between single quotation mark and double quotation mark ：
- Single quotation marks cannot explain variables
- Case study ：
#!/bin/bash
# Author: renshanwen
user="liangshan"
full_name=' I am a :${user}'
full_name2=" I am a :${user}"
echo $full_name
echo $full_name2
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-
- The result of the command is assigned to a variable ：
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- Variable =$( command )
- A read-only variable ：
- readonly Variable name
- Delete variables ：
- unset Variable name
2.3： shell Special variables ：
Variable | meaning |
$0 | The name of the current script . |
$n | Parameters passed to the script ： $1 That's the first parameter . |
$# | The number of parameters passed to the script . |
$* | All parameters passed to the script . |
All parameters passed to the script . It is slightly different when it is enclosed in double quotation marks . | |
$? | Exit status of last command / The return value of the function . General order 0 It means success ,1 It means failure .s |
$$ | At present shell The process of ID |
- Case study ：
[email protected]:~$ ./test.sh aaa bbb
File Name: ./test.sh
First Parameter: aaa
Second Parameter: bbb
Quoted Values: aaa bbb
Quoted Values: aaa bbb
Total Number of Parmaeters: 2
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* #!/bin/bash
# Author: renshanwen
echo "File Name: $0"
echo "First Parameter: $1"
echo "Second Parameter: $2"
echo "Quoted Values: [email protected]"
echo "Quoted Values: $*"
echo "Total Number of Parmaeters: $#"
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$* and [email protected] The difference between :
#!/bin/bash
echo "\$*=" $*
echo "\"\$*\"=" "$*"
echo "\[email protected]=" [email protected]
echo "\"\[email protected]\"=" "[email protected]"
echo "print each param from \$*"
for var in $*
do
echo "$var"
done
echo "print each param from \[email protected]"
for var in [email protected]
do
echo "$var"
done
echo "print each param from \"\$*\""
for var in "$*"
do
echo "$var"
done
echo "print each param from \"\[email protected]\""
for var in "[email protected]"
do
echo "$var"
done
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$*= a b c d
"$*"= a b c d
[email protected]= a b c d
"[email protected]"= a b c d
print each param from $*
a
b
c
d
print each param from [email protected]
a
b
c
d
print each param from "$*"
a b c d
print each param from "[email protected]"
a
b
c
d
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-
$* When surrounded by double quotes , The printed parameters are a whole . however [email protected] It will print out a single parameter .
2.4： Replace ：
#!/bin/bash
# Author: renshanwen
a=10
echo -e "Value is $a \n"
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- Meaning of escape character
- Command substitution ：
#!/bin/bash
# Author: renshanwen
DATA=`date`
echo "Data is $DATA"
USERS=`who | wc -l`
echo "Logged in user $USERS"
UP=`date ; uptime`
echo "UP time is $UP"
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- Command substitution means Shell You can execute the order first , Save the output temporarily , Output... In the right place .
- Variable substitution ：
2.5： character string ：
- Single quotation marks
- Double quotes ：
- Double quotes can have variables , Escape characters can also appear .
- String splicing ：
#!/bin/bash
# Author: renshanwen
my_name="liangshan"
my_full_name=" name : "$my_name"！"
echo $my_full_name
Running results ：
[email protected]:~$ ./test.sh
name : liangshan！
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#!/bin/bash
# Author: renshanwen
my_name="liangshan"
my_full_name=" name : ${my_name}！"
echo $my_full_name
[email protected]:~$ ./test.sh
name : liangshan！
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- You can use quotation marks , You can also use ${}
- Get string length ：
#!/bin/bash
# Author: renshanwen
my_name="liangshan"
my_full_name=" Name length : ${#my_name}！"
echo $my_full_name
Running results ：
[email protected]:~$ ./test.sh
Name length : 9！
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- ${# Variable name }
- Extract substring ：
#!/bin/bash
# Author: renshanwen
my_name="liangshan"
echo ${my_name:0:5}
# Output : liang
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- ${ Variable name ： Start subscript ： Number }
2.6： Array ：
- 1： To define an array ：
- array_name=(value1 value2), Note that there is no comma between variables .
- array_name[0]=value1
- 2: Read array ：
- ${ Array name [index]}
- Get all the elements in the array ： ${ Array name [*]}
- 3： Gets the length of the array ：
- ${# Array name [*]}
#!/bin/bash
# Author: renshanwen
my_array=("1" "2" "3")
echo " The first element of the array is ： ${my_array[0]}"
echo " All elements of the array are : "${my_array[*]}
echo " The length of the array is ：${#my_array[*]}"
[email protected]:~$ ./test.sh
The first element of the array is ： 1
All elements of the array are : 1 2 3
The length of the array is ：3
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2.7： Operator ：
- Arithmetic operator ：
- We use it a lot expr Do arithmetic operations ：
- Space between expression and operator .
- The complete expression uses `` contain .
#!/bin/bash
# Author: renshanwen
val=`expr 2 + 2`
echo " The result is ：$val"
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List of arithmetic operators ：
- Relational operator ：
- Relational operators only support ： Numbers , String not supported .
- Boolean operator ：
- String operators ：
Two ： shell Branch loop
2.1： Conditional branch ：
- 1： The simplest if sentence ： a It's not equal to b The output .
#!/bin/bash
# Author: renshanwen
a=10
b=20
if [ $a != $b ]
then
echo "a is not equal to b"
fi
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- 2： if else sentence ：
#!/bin/bash
# Author: renshanwen
a=10
b=10
if [ $a != $b ]
then
echo "a is not equal to b"
else
echo "a is equal to b"
fi
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- 3: Multi branch selection structure ：
#!/bin/bash
# Author: renshanwen
a=10
if [ $a -lt 10 ]
then
echo "a Less than 10"
elif [ $a -lt 20 ]
then
echo "a Less than 20, Greater than or equal to 10"
else
echo "a Greater than 20"
fi
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- 4: And test Use with commands ：
#!/bin/bash
# Author: renshanwen
a=$[10*20]
b=$[20*10]
if test $[a] -eq $[b]
then
echo " Both equal "
else
echo " The two are not equal "
fi
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2.2： loop ：
- 1: Use while Loop printing 1 To 100
#!/bin/bash
# Author: renshanwen
COUNTER=0
while [ $COUNTER -lt 100 ]
do
COUNTER=`expr $COUNTER + 1`
echo $COUNTER
done
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- 2: Use while Loop reading variable information ：
#!/bin/bash
# Author: renshanwen
while read FILM
do
echo " The input is ：$FILM"
done
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- Keyboard input information , Save in variables ： FILM in .
- Press Ctrl + D End of cycle .
- 3： until loop ：
- Not until a certain condition is established .
- Case study ： Print 0 To 10
#!/bin/bash
# Author: renshanwen
COUNT=0
until [ $COUNT -gt 10 ]
do
echo $COUNT
COUNT=`expr $COUNT + 1`
done
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- 4: for loop ：
#!/bin/bash
# Author: renshanwen
for loop in 1 2 3 4 5
do
echo "loop The value of is $loop"
done
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- 5： Out of the loop ：
- break
- comtinue
3、 ... and ： Enhanced output , test , Output and input redirection
3.1： Enhanced Edition echo—printf
- And C The language format is the same .
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3.2: test command ：
- Check whether a certain condition is true .
- Case a ： Test whether the two numbers are equal ( The judgment is the value )：
num1=100
num2=100
if test $[num1] -eq $[num2]
then
echo 'The two numbers are equal!'
else
echo 'The two numbers are not equal!'
fi
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- Case 2 ： Test whether two characters are equal .
num1=100
num2=100
if test num1=num2
then
echo 'The two strings are equal!'
else
echo 'The two strings are not equal!'
fi
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3.3： Output , Input redirection
- Output of command , Input redirection ：
-
>： Cover the output -
>>: Additional output -
<: Override input
Four ： function
- 1： Must be defined before using .
- 2： shell The return value of a function can only be an integer , Generally speaking 0 It means success , Other indication of failure .
- 3： If you need to return other types , You need to define a variable first , The script can access this variable when necessary .
- 4: Case a ： Define a function , And then call .
#!/bin/bash
# Author: renshanwen
Hello () {
echo " Ha ha ha "
}
Hello
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- 2： Case 2 ： Define a function with a return value , And then call .
#!/bin/bash
# Author: renshanwen
funcWithReturn (){
read aNum
read anotherNum
return $(($aNum + $anotherNum))
}
funcWithReturn
res=$?
echo $res
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- Be careful ： Cannot return a string , Need to use $() Convert to variable .
- $? You can retrieve the return value of the last command .
- 3: Nested use of functions ：
#!/bin/bash
# Author: renshanwen
func_one (){
echo " The first function "
func_two
}
func_two (){
echo " The second function "
}
func_one
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- 4: Function to get parameters ：
func_one (){
echo " The first parameter is $1"
echo " The second parameter is $2"
}
func_one aaa bbb
[email protected]:~$ ./test.sh
The first parameter is aaa
The second parameter is bbb
[email protected]:~$
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