linux shell变量$#,$@,$0,$1,$2的含义解释

变量说明: 
$$ Shell本身的PID（ProcessID） 
$! Shell最后运行的后台Process的PID 
$? 最后运行的命令的结束代码（返回值） 
$- 使用Set命令设定的Flag一览 
$* 所有参数列表。 所有的参数被认为是一个字符串
$@ 所有参数列表。参数是独立的字符串
$# 添加到Shell的参数个数 
$0 Shell本身的文件名 
$1～$n 添加到Shell的各参数值。$1是第1个参数、$2是第2个参数…。

通过一个脚本，来看看各个变量的效果

 #!/bin/sh

 ## RustFisher

 echo "----------------------"
 echo "PID:            \$$  $$"
 echo "option numbers: \$#  $#"
 echo "last return:    \$?  $?"
 echo "all parameters: \$*  $*"
 echo "all parameters: \$@  $@"
 echo "file name:      \$0  $0"
 echo "1st param:      \$1  $1"
 echo "2nd param:      \$2  $2"
 echo "3rd param:      \$3  $3"
 echo "4th param:      \$4  $4"
 echo "9th parem:      \$9  $9"
 echo "-----------------------"

 index=

 echo "get args by \"\$@\":"

 for arg in "$@"
 do
 echo "Arg #$index=$arg"
 let "index+=1"
 done

 echo "-----------------------"

 index=

 echo "get args by \"\$*\":"

 for arg in "$*"
 do
 echo "Arg #$index=$arg"
 done

 echo "-----------------------"

输出结果：

$ sh show.sh dont "worry be" happy
----------------------
PID:            $$
option numbers: $#  

all parameters: $*  dont worry be happy
all parameters: $@  dont worry be happy
  show.sh
1st param:      $  dont
2nd param:      $  worry be
3rd param:      $  happy
4th param:      $
9th parem:      $
-----------------------
get args by "$@":
Arg #=dont
Arg #=worry be
Arg #=happy
-----------------------
get args by "$*":
Arg #=dont worry be happy
-----------------------