One-Day Study Shell: Part 1 The first Shell & Shell Variable & String & Array & Comment

悠悠 2022-10-09 06:30 18阅读 0赞

### One-Day Study Shell : Part 1 ###

*  The first Shell
 *  Shell Variable
 *  Shell String
 *  Shell Array
 *  Shell Comment

# The first Shell #

*  **Create a new file “hello.sh”, write codes :**

#!/bin/bash
    echo "Hello Shell !"

*  **Run Shell: `cd` to the directory of the file "hello.sh"**

chmod +x ./hello.sh
    ./hello.sh

*  **Output:**

![在这里插入图片描述][20210624120207940.png_pic_center]

# Shell Variable #

*  **Rule1: Only English,number(cannot be the first), and\_**
 *  **Rule2: No space**
 *  **Rule3: No punctuation(,./~…)**
 *  **Rule4:No keywords in bash(`bash --help`)**

Valid variable
    KATHY
    Kathy_Wang
    _kathy
    kathy16

Invalid variable
    16kathy
    ?kathy

*  **Define variables**

# no sapce between variable name and "="
    name="kathy"

*  **Assign value to variable**

#1.direct assign value
    name="kathy"
    #2.use statement 
    for file in $(ls /sys)

*  **Use variable** : `echo $variable`

name="kathy"
    #Method 1
    echo $name
    #Method 2
    echo ${ name}

*  **Read-only variable**  
    use `readonly` to set the variable to read-only variable, the value of read-only variable can not be changed

#!/bin/bash
    name="kathy"
    echo ${ name}
    readonly name
    name="keke"

![在这里插入图片描述][20210624143852800.png_pic_center]

*  **Delete variable** **`unset variable_name`**

#!/bin/bash
    name="kathy"
    unset name
    echo ${ name}

![在这里插入图片描述][20210624144210853.png_pic_center]

*  **Variable types**  
    1.Local variable  
    2.Environment variable  
    3.shell variable

# Shell String #

*  **Apostrophe `''`**  
    Just output in ‘’, cannot use variable

#!/bin/bash
    name="kathy"
    str='Your name is \"$name\"! \n'
    echo $str

![在这里插入图片描述][20210624145157946.png_pic_center]

*  **Double quotes`'' ''`**  
    Can use variable and escape character

#!/bin/bash
    name="kathy"
    str="Your name is \"$name\"! \n"
    echo $str

![在这里插入图片描述][20210624145450154.png_pic_center]

*  **Get string length `echo ${#string_name}`**

#!/bin/bash
    str="name"
    echo ${ #str}

![在这里插入图片描述][20210624145751447.png_pic_center]

*  **Extract substring `echo ${string_name:from:to}`**

#!/bin/bash
    str="What is your name?"
    echo ${ str:2:6}

![在这里插入图片描述][2021062415014757.png_pic_center]

*  **Find string \`echo `expr index "$string_name" wanted_char`**

#!/bin/bash
    str="What is your name?"
    echo `expr index "$str" t`

![在这里插入图片描述][20210624150635743.png_pic_center]

# Shell Array #

bash supports just one-dimensional array(no multi-dimensional array), and there is no limit to the size of the array.

*  **Define array `array_name=(value0 value1 value2)`**

# Method1
    array_name=(
    value0
    value1
    value2
    )
    
    #Method2
    array_name[0]=value0
    array_name[1]=value1
    array_name[2]=value2

*  **Read array `${array_name[index]}`**  
    Get all elements in array by `echo ${array_name[@]}`

#!/bin/bash
    array_name=(name age school)
    echo ${ array_name[1]}

![在这里插入图片描述][20210624152246855.png_pic_center]

#!/bin/bash
    array_name=(name age school)
    echo ${ array_name[@]}

![在这里插入图片描述][20210624152347195.png_pic_center]

*  **Get array length `${#array_name[@]}`**

#!/bin/bash
    array_name=(name age school)
    _1st_method_array_length=${ #array_name[@]}
    _2nd_method_array_length=${ #array_name[*]}
    single_element_length=${ #array_name[2]}
    echo ${ _1st_method_array_length}
    echo ${ _2nd_method_array_length}
    echo ${ single_element_length}

![在这里插入图片描述][20210624153540104.png_pic_center]

# Shell Comment #

*  **Add `#`to each line**

#-------------------------
    #Name
    #author:
    #site:
    #-------------------------
    ##### start #####
    #
    #
    # some comments
    ##### end #####

*  **Multi-line comment**

:<<EOF
    Comment content...
    Comment content...
    Comment content...
    EOF

[20210624120207940.png_pic_center]: /images/20221005/807c70eca97f4f28855fb284dafa8cb3.png
[20210624143852800.png_pic_center]: /images/20221005/733c793439a24d18a3103f3cb3fbf6bc.png
[20210624144210853.png_pic_center]: /images/20221005/76a3083dd252423e9695c08ed3f0e092.png
[20210624145157946.png_pic_center]: /images/20221005/8dc857e3c3954906ac78315223e7e94e.png
[20210624145450154.png_pic_center]: /images/20221005/943661a7da8148e4840167be3667c9b2.png
[20210624145751447.png_pic_center]: /images/20221005/2e4321a0356346a8b58ea93a798208ab.png
[2021062415014757.png_pic_center]: /images/20221005/2ff4d498c3e34b2c8106df4603b8f368.png
[20210624150635743.png_pic_center]: /images/20221005/862eedc4ac4a489f992e85c508109042.png
[20210624152246855.png_pic_center]: /images/20221005/073e2997e4d249bc99f47f25694378de.png
[20210624152347195.png_pic_center]: /images/20221005/ae7238e7adf845839cacd454ec1b39fa.png
[20210624153540104.png_pic_center]: /images/20221005/c8fb6b38bab04358a26e3f086e2acac7.png