帮忙解释一下 谢谢

leohuangfu

#!/bin/bash
#program:
# user can keyin filename to touch 3 ne files.
#history:
#2006/12/04 huangfu first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
echo -e "i will use 'touch' command to create 3 files ."
read -p " please input the filename what you want : " fileuser
filename=${fileuser:-"filename"}   ＃这一行啥意思啊 迷茫啊 哪位高人解释一下。
date1=`date -d "-2 day " +%Y%m%d`
date2=`date -d "-1 day " +%Y%m%d`
date3=`date +%Y%m%d`
file1="$filename""_""$date1"
file2="$filename""_""$date2"
file3="$filename""_""$date3"
touch $file1
touch $file2
touch $file3

yongjian

if fileuser not set or it is empty, use the value "filename". please see bash manual on parameter substitution and expansion.

huan

对比一下

1. 
   
2. [0 No.2007 huan@huan ~]$ unset filename fileuser
   
3. 
   
4. [0 No.2008 huan@huan ~]$ filename=${fileuser:-"filename"}
   
5. 
   
6. [0 No.2009 huan@huan ~]$ echo $filename
   
7. filename
   
8. 
   

复制代码

1. 
   
2. [0 No.2010 huan@huan ~]$ fileuser="hello world"
   
3. 
   
4. [0 No.2011 huan@huan ~]$ filename=${fileuser:-"filename"}
   
5. 
   
6. [0 No.2012 huan@huan ~]$ echo $filename
   
7. hello world
   
8. 
   
9. 
   

复制代码

leohuangfu

也就是说 为了防止用户随意的敲回车键，用变量的方式 让filename的值默认为filename
多谢 huan  yongjian 2为帅哥 谢谢。

xihai

是“:-”还是“:=”??

leohuangfu

是：－  我现在明白这条语句的意思，但是具体的用法不太明白。