连载shell（二）：test判断，判断符号[ ]，shell script的默认变量（$0， $1...），shift参数变量偏移

1.利用test命令的测试功能：
需求：
让用户输入一个文件名，我们判断：
1）这个文件是否存在，若不存在则给予一个“Filename does not exist”的信息，并中断程序；
2）若这个文件存在，则判断它是个文件或目录，结果输出“Filename is regular file”或“Filename is directory”;
3）判断一下，执行者的身份对这个文件或目录所拥有的权限，并输出权限数据。

debian@debian-pc:~/scripts$ vim sh05.sh  1 #!/bin/bash  8 #1.让用户输入文件名，并且判断用户真的有输入字符串  9 echo -e "Please input a filename, I will check the filename's type and permissions. \n\n" 10 read -p "Input a filename : " filename 11 test -z $filename && echo "You MUST input a filename." && exit 0 12  13 #2.判读文件是否存在，若不存在则显示信息并结束脚本 14 test ! -e $filename && echo "The filename '$filename' DO NOT exist" && exit 0 15  16 #3.开始判断文件类型及属性 17 test -f $filename && filetype = "regulare file" 18 test -d $filename && filetype = "directory" 19 test -r $filename && perm = "readable" 20 test -w $filename && perm = "perm writable" 21 test -x $filename && perm = "perm executable" 22  23 #4.开始输出信息 24 echo "The filename: $filename is a $filetype" 25 echo "And the permissions are : $perm"

*************************************************************#不输入任何字符，结果如下：debian@debian-pc:~/scripts$ ./sh05.sh Please input a filename, I will check the filename's type and permissions. Input a filename : You MUST input a filename.*************************************************************#输入字符，结果如下：debian@debian-pc:~/scripts$ ./sh05.sh Please input a filename, I will check the filename's type and permissions. Input a filename : sc The filename 'sc' DO NOT exist

2.利用判断符号[]
需求：
1）当执行一个程序的时候，这个程序会让用户选择Y或N；
2）如果用户输入Y或y时，就显示“OK，continue”；
3）如果用户输入N或n时，就显示“Oh，interrupt！”；
4）如果不是Y/y/N/n之内的其他字符，就显示“I don`t know what your choice is”。

  1 #!/bin/bash  7 read -p "Please input (Y/N): " yn  8 [ "$yn" == "Y" -o "$yn" == "y" ] && echo "OK, continue..." && exit 0  9 [ "$yn" == "N" -o "$yn" == "n" ] && echo "Oh, interrupt!!" && exit 0 10 echo -e "I don't know what your choice is !?" && exit 0

debian@debian-pc:~/scripts$ ./sh06.sh Please input (Y/N): yOK, continue...debian@debian-pc:~/scripts$ ./sh06.sh Please input (Y/N): ggI don't know what your choice is !?

3.shell script的默认变量（0,1…）
需求：
1）程序的文件名；
2）共有几个参数；
3）若参数的个数小于2则告知用户参数数量太少；
4）全部的参数内容；
5）第一个参数；
6）第二个参数。

  1 #!/bin/bash  7 echo "The script name is    ==> $0"  8 echo "Total parameter number is    ==> $#"  9 [ "$#" -lt 2 ] && echo "The number of parameter is less than 2. Stop here." && exit 0 10 echo "Your whole parameter is    ==> $@" 11 echo "Test '$*'is  ==>$*" 12 echo "The 1st parameter    ==> $1" 13 echo "The 2nd parameter    ==> $2"

debian@debian-pc:~/scripts$ ./sh07.sh aa bb ccThe script name is    ==> ./sh07.shTotal parameter number is    ==> 3Your whole parameter is    ==> aa bb ccTest 'aa bb cc'is  ==>aa bb ccThe 1st parameter    ==> aaThe 2nd parameter    ==> bb

4.shift：造成参数变量号码偏移

  1 #!/bin/bash  7 echo "Total parameter number is ==> $#"  8 echo "Your whole parameter is ==> '$@'"  9 shift #进行第一次“一个变量的shift” 10 echo "Total parameter number is ==> $#" 11 echo "Your whole parameter is ==> '$@'" 12 shift 3 #进行第二次“三个变量的shift” 13 echo "Total parameter number is ==>$#" 14 echo "Your whole parameter is ==> '$@'"

debian@debian-pc:~/scripts$ ./sh08.sh one two three four five sixTotal parameter number is ==> 6Your whole parameter is ==> 'one two three four five six'Total parameter number is ==> 5Your whole parameter is ==> 'two three four five six'Total parameter number is ==>2Your whole parameter is ==> 'five six'