Linux read Befehl

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Linux read Befehl wird verwendet, um Werte von der Standard-Eingabe zu lesen.

read internes Kommando wird verwendet, um Zeilen von der Standard-Eingabe zu lesen. Dieses Kommando kann verwendet werden, um Tastatureingaben zu lesen, und kann auch Zeilen aus einer Datei lesen, wenn Redirection verwendet wird.

Syntax

read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]

Parameterbeschreibung:

• -a Folgt eine Variable, die als Array angesehen wird, und dann wird ihr ein Wert zugewiesen, Standardmäßig wird ein Leerzeichen als Trennzeichen verwendet.
• -d Folgt ein Symbol, wirklich nur der erste Zeichen dahinter ist wichtig, als Abschlusszeichen.
• -p Folgt eine Hinweisinformation, die vor dem Eingabeschritt gedruckt wird.
• -e Bei der Eingabe kann die Kommando-Vervollständigungsfunktion verwendet werden.
• -n Folgt eine Zahl, die die Länge des Eingabeplaintexts definiert, sehr nützlich.
• -r Abschaltung, wenn keine Option vorhanden ist, dann als Escape-Zeichen, bei Verfügbarkeit ist es ein normaler Zeichen.
• -s silent mode, does not display input characters on the screen, for example, entering a password during login.
• -t followed by seconds, defines the waiting time for input characters.
• -u followed by fd, reads from the file descriptor, which can be a new one opened by exec.

Online example

1, simple read

#!/bin/bash
#Here it will be a newline by default  
echo "Enter the website name: "  
#Read input from the keyboard  
read website  
echo "The website name you entered is $website"  
exit 0  #exit

Test results are:

Enter the website name: 
de.oldtoolbag.com
The website name you entered is de.oldtoolbag.com

2,-p parameter allows to specify a prompt directly in the read command line.

#!/bin/bash
read -p "Enter the website name: " website
echo "The website name you entered is $website" 
exit 0

Test results are:

Enter the website name:de.oldtoolbag.com
The website name you entered is de.oldtoolbag.com

3,-t parameter specifies the number of seconds read command waits for input, when the timer is up, the read command returns a non-zero exit status.

#!/bin/bash
if read -t 5 -p "Enter the website name: " website
then
    echo "The website name you entered is $website"
else
    echo "\nSorry, you have exceeded the time limit for input."
fi
exit 0

The executing program does not input, waiting 5 seconds later:

Enter the website name:
Sorry, you have exceeded the time limit for input

4, besides input time counting, you can also use -n Parameter settings read The command counts the input characters. When the number of input characters reaches the predetermined number, it exits automatically and assigns the input data to the variable.

#!/bin/bash
read -n1 -p "Do you want to continue [Y/N]?" answer
case $answer in
Y | y)
      echo "fine ,continue";;
N | n)
      echo "ok,good bye";;
*)
     echo "error choice";;
esac
exit 0

This example uses-n option, followed by a number 1, indicating that the read command will exit as soon as it receives a character. Just press a character to answer, and the read command will immediately accept the input and pass it to the variable without pressing the enter key.

Only accepts 2 An input will exit:

#!/bin/bash
read -n2 -p "Please enter any two characters: " any
echo "\nYou entered the two characters are:$any"
exit 0

Enter two characters to execute the program:

Please enter any two characters: 12
The two characters you entered are:12

5,-s The option can make read The data entered in the command does not appear on the command terminal (in fact, the data is displayed, but read The command sets the text color to the same as the background color). This option is commonly used when entering a password.

#!/bin/bash
read  -s  -p "Please enter your password: " pass
echo "\nYou entered the password is $pass"
exit 0

The program does not display the password after entering the password:

Please enter your password:
The password you entered is w3codebox

6.Read file

The read command will read a line of text each time it is called. When there are no more lines to read in the file, the read command will exit with a non-zero status.

How to pass the data in the file to read? Use the cat command and pass the result directly to the while command containing the read command through a pipe.

The content of the test file test.txt is as follows:

123
456
w3codebox

Test Code:

#!/bin/bash
count=1    # Assignment statement, no space
cat test.txt | while read line      # The output of the cat command is used as the input of the read command, the value of the read command after > is placed in line
do
   echo "Line $count:$line"
   count=$[ $count + 1 ]          # Note the space in the brackets.
done
echo "finish"
exit 0

Execution result is:

Line 1:123
Line 2:456
Line 3:w3codebox
finish

Use -e Parameter, the following example input character a Press Tab Press the key and the relevant filenames (existing in the directory) will be output:

$ read -e -p "Enter the filename:" str 
Enter the filename: a
a.out    a.py     a.pyc    abc.txt  
Enter the filename: a

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