4shell中的特殊变量

 test.sh

1. #!/bin/bash
2. echo "Language: $1"
3. echo "URL: $2"

运行

. ./test.sh Shell http://www.baidu.com/

结果

Language: Shell URL: http://www.baidu.com/

Shell是第一个位置参数，http://www.baidu.com/是第二个位置参数，两者之间以空格分隔

 给函数传递位置参数

test.sh

1. #!/bin/bash
2. #定义函数
3. function func(){
4. echo "Language: $1"
5. echo "URL: $2"
6. }
7. #调用函数
8. func C++ http://www.baidu.com//

. ./test.sh

Language: C++
URL: http://www.baidu.com/

test.sh

1. #!/bin/bash
2. echo ‘------------test special variable in file---------‘
3. echo "file name:${0}"
4. echo "first para:${1}"
5. echo "second para:${2}"
6. echo "all paras:$*"
7. echo "paras Num:$#"
8. echo "current PID:$$"
9. echo "PPID:$PPID"

执行bash test.sh aa bb

结果

1. ------------test special variable in file---------
2. file name:test.sh
3. first para:aa
4. second para:bb
5. all paras:aa bb
6. paras Num:2
7. current PID:79494
8. PPID:91647

test.sh

1. #!/bin/bash
2. echo ‘------------test special variable in function---------‘
3. function test_special_variable(){
4. echo "file name:${0}"
5. echo "first para:${1}"
6. echo "second para:${2}"
7. echo "all paras:$*"
8. echo "paras Num:$#"
9. echo "current PID:$$"
10. echo "PPID:$PPID"
11. }
12. test_special_variable aa bb

执行bash test.sh

结果

1. ------------test special variable in function---------
2. file name:test.sh
3. first para:cc
4. second para:dd
5. all paras:cc dd
6. paras Num:2
7. current PID:79494
8. PPID:91647

test.sh

1. #!/bin/bash
2. echo ‘print each para from "$*"‘
3. for var in "$*"
4. do
5. echo "$var"
6. done
7. echo ""

执行bash test.sh aa bb

print each para from "$*"

aa bb

test.sh

1. #!/bin/bash
2. echo ‘print each para from  $*‘
3. for var1 in $*
4. do
5. echo "$var1"
6. done
7. echo ""

print each para from  $*

aa

bb

test.sh

1. #!/bin/bash
2. echo ‘print each para from ""‘
3. for var2 in ""
4. do
5. echo $var2
6. done
7. echo ""

print each para from ""

aa

bb

test.sh

1. #!/bin/bash
2. echo ‘print each para from ‘
3. for var3 in 
4. do
5. echo $var3
6. done
7. echo ""

print each para from

aa

bb

$? 获取上一个命令的退出状态

 test.sh

1. #!/bin/bash
2. if [ "$1" == 100 ]
3. then
4. exit 0 #参数正确，退出状态为0
5. else
6. exit 1 #参数错误，退出状态1
7. fi

exit表示退出当前 Shell 进程，我们必须在新进程中运行 test.sh，

否则当前 Shell 会话（终端窗口）会被关闭，我们就无法取得它的退出状态。

运行脚本：bash ./test.sh 100 #使用bash作为一个新进程运行

获取退出状态：echo $?----->0

运行脚本：bash ./test.sh 89

获取退出状态：echo $?----->1

$? 获取函数的返回值

test.sh

1. #!/bin/bash
2. #得到两个数相加的和
3. function add(){
4. return `expr $1 + $2`
5. }
6. add 23 50 #调用函数
7. echo $? #获取函数返回值