Read of the shell command

read:

Brief introduction:

The read command reads the value of a variable from the keyboard and is typically used in a shell script to interact with the user. The command can read the values of multiple variables at once, and the variables and input values need to be separated by spaces. After the read command, if no variable name is specified, the read data is automatically assigned to the specific variable reply.

Grammar

Read (options) (parameter

Options

Read can be available with-a,-D,-E,-N,-p,-r,-T, and-s eight options.

-A: Read content into numeric values

Echo-n "Input muliple values into an array:"

Read-a Array

-D: Represents the delimiter, the delimiter, which is normally the interval of the IFS parameter, but through-D, we can define the character position that reads until execution occurs. For example Read–d Madfds value, when reading a character with M, does not continue to read backwards, for example, the input is Hello m, the valid value is "Hello", please note that the space in front of the m will be deleted. You can enter multiple strings in this way, such as define "." As a knot symbol and so on.

-e: Only for scripts that interact with each other, and it uses ReadLine to collect input rows. Read these few words don't understand what meaning, first skip.

-N: Used to limit the maximum number of characters that can be read in as valid. For example Echo–n 4 value1 value2, if we try to enter 12 34, then only the previous valid 12 3, as input, in fact, after you enter the 4th character ' 3 ', automatically end the input. The result here is value 12,value2 of 3.

-P: For the prompt, in the previous example we used the Echo–n "..." to give a prompt, you can use the Read–p ' ... my promt? ' The way value is represented by just one statement.

-r: In the parameter input, we can use the '/' to indicate that there is no input, newline continues to enter, if we need to line the last '/' as a valid character, can be done through-R. Also in the input characters, we want special characters such as/n to take effect, and the-r option should also be used.

-S: For some special symbols, such as arrows, do not print them on the terminal, such as Read–s key, we press the cursor, after the carriage return, if we ask to display, that is, ECHO, the cursor upward, if not using-s, at the input, the input display ^[[a, That is, print on the terminal, and then if ECHO is required, the cursor will move up.

-T: Used to indicate the time to wait for input, in seconds, to wait longer, to continue execution of subsequent scripts, and note that the parameter retains its original value as null input.

Parameters

Variable: Specifies the variable name of the Read value.

Example 1:

Read input from standard input and assign value to name

# Read Name

Sxzhou

Print variable name

# echo $name

Sxzhou

Example 2:

-P Specify prompt

# read-p "Input your name:" Name

Input your Name:sxzhou

# echo $name

Sxzhou

Example 3:

Specifying multiple variables

# read-p "Input animal name:" Cat Dog

Input Animal Name:tom Flower

# echo $cat

Tom

# echo $dog

Flower

Example 4:

If a variable is not specified in the Read command, then the read name places any data it receives in the special environment variable reply

# Read

This is reply

# echo $REPLY

This is reply

Example 5:

Using reply to find factorial

# VI product.sh

#!/bin/bash

Read-p "Enter a number:"

Product=1

for ((count=1; count<= $REPLY; count++))

Do

product=$[$product * $count]

Done

echo "The product of $REPLY is $product"

# sh product.sh

4

The product of 4 is 24

Attention:

There is a space between the parenthesis and the bracket symbol and the content

No spaces on both sides of the equals sign

Example 6:

Timeout Test read-t

# VI overtime.sh

#!/bin/bash

If read-t 5-p "Please enter your name:" Name

Then

echo "Hello $name, welcome!"

Else

Echo

echo "Sorry, too slow! Please retry "

Fi

Enter a name in five seconds

# sh overtime.sh

Please enter your name:

Sxzhou

Hello Sxzhou, welcome!

Five seconds away

# sh overtime.sh

Please enter your name:

Sorry, too slow! Please retry

Example 7:

The read command determines the input

# VI decide.sh

#!/bin/bash

Read-n1-p "Do you want to continue [Y (y)/n (n.)]?" Answer

Case $answer in

Y | Y) echo

echo "Fine, continue ...";;

N | N) Echo

echo "Ok,goodbay"

exit;;

Esac

# sh decide.sh

Do you want to continue [Y (y)/n (n.)]? Y

Fine, continue ...

# sh decide.sh

Do you want to continue [Y (y)/n (n.)]? N

Ok,goodbay

Note:

-n1 Enter a character for the limit

Example 8:

Hide Input Read-s

# VI hide.sh

#!/bin/bash

Read-s-P "Enter your passwd:" Pass

Echo

echo "Is your passwd readlly $pass?"

# sh hide.sh

Enter your passwd: (input 123456, not shown)

Is your passwd readlly 123456?

Example 9:

# VI text.sh

#!/bin/bash

Count=1

Cat hide.sh | While Read line

Do

echo "line $count: $line"

count=$[$count + 1]

Done

echo "Finished processing the file"

# sh text.sh

Line 1: #!/bin/bash

Line 2:read-s-P "Enter your passwd:" Pass

Line 3:echo

Line 4:echo "is your passwd readlly $pass?"

Read of the shell command