Shell中特殊的变量

$表示当前的进程，当使用echo $$是会输出当前shell的pid

1 echo $$

脚本文件varlist.sh

1 #!/bin/bash
2
3 echo "File name: $0"
4 echo "First parameter: $1"
5 echo "Second Parameter: $2"
6 echo "Quoted Values: [email protected]"
7 echo "Quoted Values: $*"
8 echo "Total Number of Parameter : $#"

执行varlist.sh hello world结果输出如下：

$ sh ./varlist.sh hello world
File name: ./varlist.sh
First parameter: hello
Second Parameter: world
Quoted Values: hello world
Quoted Values: hello world
Total Number of Parameter : 2

$*与[email protected]的区别：

当使用""是会出对于他们存在差异，"$*" 会将所有的参数作为一个整体，以"$1 $2 … $n"的形式输出所有参数；"[email protected]" 会将各个参数分开，以"$1" "$2" … "$n" 的形式输出所有参数。 看下面的例子：

 1 #!/bin/bash
 2 #description: use variable
 3 #Author: blacksonny
 4 #Copyright (c)
 5 #Script follows here:
 6
 7 echo "\$*=" $*
 8 echo "\"\$*\"=" "$*"
 9
10 echo "\[email protected]=" [email protected]
11 echo "\"\[email protected]\"=" "[email protected]"
12
13 echo "print each param from \$*"
14 for var in $*
15 do
16     echo "$var"
17 done
18
19 echo "print each param from \[email protected]"
20 for var in [email protected]
21 do
22     echo "$var"
23 done
24
25 echo "print each param from \"\$*\""
26 for var in "$*"
27 do
28     echo "$var"
29 done
30
31 echo "print each param from \"\[email protected]\""
32 for var in "[email protected]"
33 do
34     echo "$var"
35 done

输出结果：

 1 $ sh ./varcompare.sh "a" "b" "c" "d"
 2 $*= a b c d
 3 "$*"= a b c d
 4 [email protected]= a b c d
 5 "[email protected]"= a b c d
 6 print each param from $*
 7 a
 8 b
 9 c
10 d
11 print each param from [email protected]
12 a
13 b
14 c
15 d
16 print each param from "$*"
17 a b c d
18 print each param from "[email protected]"
19 a
20 b
21 c
22 d

退出状态：

$? 可以获取上一个命令的退出状态。所谓退出状态，就是上一个命令执行后的返回结果。
退出状态是一个数字，一般情况下，大部分命令执行成功会返回 0，失败返回 1。