Filename =$ {fileuser:-"filename "}

Filename $ {fileuser:-& quot; filename & quot;} -- Linux general technology-Linux technology and application information. Read the following for details. #! /Bin/bash
# Program:
# User can keyin filename to touch 3 new files.
# History:
#2005/08/23 VBird First release
PATH =/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin :~ /Bin
Export PATH

#1. Ask the user to enter the file name and obtain the fileuser variable;
Echo-e "I will use 'touch' command to create 3 files ."
Read-p "Please input the filename what you want:" fileuser

#2. To prevent users from pressing Enter at will, does the variable function show whether the file name is set?
Filename =$ {fileuser:-"filename "}

#3. start to use the date command to obtain the required file name;
Date1 = 'date -- date = '2 days ago '+ % Y % m % d'
Date2 = 'date -- date = '1 days ago '+ % Y % m % d'
Date3 = 'date + % Y % m % d'
File1 = "$ filename" "$ date1"
File2 = "$ filename" "$ date2"
File3 = "$ filename" "$ date3"

#4. Create a file name!
Touch $ file1
Touch $ file2
Touch $ file3
Could you tell me the above:
#2. To prevent users from pressing Enter at will, does the variable function show whether the file name is set?
Filename =$ {fileuser:-"filename "}
Why ?????