shell脚本的参数问题

一个简单例子

para.sh
########################
#!/bin/sh
#scriptname:para

echo "this script is call $0"
echo "$0 $1 $2"
echo "The number of positionalparameters is $#"

echo "$* is the dollar star"

echo "$@ is the dollar at"

echo " "$*" is the dollar star which has quoation marks"

echo " "$@" is the dollar at which has quoation marks"
################
[root@yqrh5u2]chmod +x para.sh
[root@yqrh5u2 rbf]# ./para.sh 1st_name 2nd_para 3rd_last
this script is call ./para.sh
./para.sh 1st_name 2nd_para
The number of positionalparameters is 3
1st_name 2nd_para 3rd_last is the dollar star
1st_name 2nd_para 3rd_last is the dollar at
1st_name 2nd_para 3rd_last is the dollar star which has quoation marks
1st_name 2nd_para 3rd_last is the dollar at which has quoation marks




Positional Parameter What It References

$0 References the name of the script,脚本的名称

$# Holds the value of the number of positional parameters，参数的个数

$* Lists all of the positional parameters，列出所有的参数

$@ Means the same as $*, except when enclosed in double quotes

"$*" Expands to a single argument (e.g., "$1 $2 $3")，

"$@" Expands to separate arguments (e.g., "$1" "$2" "$3")

$1 .. $9 References up to nine positional parameters，应用对应的参数


$* and $@ 区别，只有单他们有双引号是才有区别：
$ set 'apple pie' pears peaches

6 $ for i in $@
> do
> echo $i
> done

apple
pie
pears
peaches



7 $ set 'apple pie' pears peaches
8 $ for i in "$@" # At last!!
> do
> echo $i
> done

apple pie
pears
peaches



脚本的参数至少是1，
name=${1:?"requires an argument" }

echo Hello $name
:? 将会检验$1是否有值，加入没有，脚本退出，并且报错误信息。