Shell built-in commands

1 Read

1.1 Introduce

read yes Shell Built in commands , Used to read data from standard input and assign it to variable . If there is no redirection , The default is to read the data entered by the user from the terminal console ; If redirected , Then you can read data from the file .

1.2 grammar

read [-options] [var1 var2 ...]

options Supported parameters :

Options	explain
-a array	Assign the read data to the array array, From the subscript 0 Start .
-d delimiter	Use string delimiter Specify the position where the reading ends , Instead of a newline （ The data read does not include delimiter）.
-e	When getting user input , Code conversion of function keys , The character corresponding to the function key will not be directly explicit .
-n num	Read num Characters , Instead of a whole line of characters .
-p prompt	Display prompt message , The tip is prompt.
-r	Read as is （Raw mode）, Do not interpret backslash characters as escape characters .
-s	silent mode （Silent mode）, The entered characters will not be displayed on the screen . When entering passwords and other confirmation information , It is necessary to .
-t seconds	Set timeout , The unit is in seconds . If the user does not complete the input within the specified time , that read Will return a non 0 The exit status of , Indicates a read failure .
-u fd	Use file descriptors fd As an input source , Instead of standard input , Similar to redirection .

1.3 demo

1 Use read Command assigns values to multiple variables

#!/bin/bash
read -p " Please enter a name 、 Age 、 hobby :" name age hobby

echo " full name : ${name}"
echo " Age : ${age}"
echo " hobby : ${hobby}"

2 Read a character

#!/bin/bash
read -n 1 -p " Are you sure you want to delete the user's data ? (y/n):" char
echo
echo " The character you entered is : ${char}"

3 Check the password
5 Seconds to verify whether the passwords are consistent

#!/bin/bash
read -t 5 -sp " Input password (5 Seconds ):" pwd1
echo
read -t 5 -sp " Please confirm the password (5 Seconds ):" pwd2
echo

echo "pwd1:${pwd1}, pwd2:${pwd2}"

if
         [ $pwd1 == $pwd2 ]
then
        echo " The password is the same "
else
        echo " Validation failed , Password inconsistency "
fi

2 Exit

2.1 Introduce

exit Used to exit the current Shell The environment process ends running , And you can return a status code . In general use $? You can get the exit status code

2.2 usage

#  The default return status code 0,  Generally, it means that the command is executed successfully 
exit  

#  Range of digital recommendations 0~255,   Generally, it means that the command execution fails 
exit  Not 0 Numbers   

2.3 demo

#!/bin/bash
echo "hello"
exit
echo "world"            

3 declare

declare The command is used to declare shell Variable , Implement associative array variables .

3.1 grammar

Associative arrays are also called “ Key value pair （key-value）” Array , key （key） That is, array subscript in string form , value （value） That is, the element value .

declare -A Associative array variable name =([ character string key1]= value 1 [ character string key2]= value 2 …)

Get specified key Value ：

${ Associative array variable name [key]}

Get all values ：

${ Associative array variable name [*]} #  The way 1
${ Associative array variable name [@]} #  The way 2

3.2 demo

#!/bin/bash
declare -A array=([name]=" Zhang San " [age]=14)

echo ${
    array[name]}
echo ${
    array[age]}
echo ${
    array[*]}