shell 基本编程

Posted 2020-12-26 ericguoxiaofeng

最基本：记住前面的：#!/bin/bash；以及文件后缀名一般都是.sh

[[email protected] scripts]# vi helloworld.sh 
#!/bin/bash
echo "hello world"

 然后记得给脚本添加权限，因为默认是读写权限罢了；默认给全部人添加权限：

chmod +x helloworld.sh 

 在当前目录下，两种方法执行该脚本

./helloworld.sh
sh helloworld.sh

 如果非当前目录，例如上一级目录，则：记得注意空格哦：

sh scripts/helloworld.sh 
./scripts/helloworld.sh

 --------------------------------------set--------------------------------------------

得到当前所有变量。例如：

[[email protected] scripts]# set | grep HOME
HOME=/root
JAVA_HOME=/usr/local/jdk1.8.0_181

 另外：注意PWD；不同的路径下输出的值不一样，输出的值为当前路径

----------------------------------------变量---------------------------------------------------

单引号或者双引号只是为了让空格也变成一个整体

[[email protected] scripts]# param=xiaofeng
[[email protected] scripts]# echo param
param
[[email protected] scripts]# param02="xiao feng02";param03=‘xaio feng03‘;
[[email protected] scripts]# echo $parma02;echo $param03

xaio feng03

 单双引号的区别：这里双引号脱意了，单引号并没有，爽引号更强大

[[email protected] scripts]# echo "$param02";echo ‘$param02‘;
xiao feng02
$param02

 例子，知道  STR="hello world" 想用其打印“hello worlds is greater”注意那里有个S。应该：

[[email protected] scripts]# STR="helloworld"
[[email protected] scripts]# echo ${STR}s is great
helloworlds is great

 用大括号括住

-----------------------------------export以及shell-----------------------------------------------------------------------

a 和 b 在不同的进程，所以b无法共享a的变量

[[email protected] scripts]# cat a.sh
#!/bin/bash
a=hahaha
echo "in a-----"$a
[[email protected] scripts]# cat b.sh
#!/bin/bash
./a.sh
echo "in b-----"$a
[[email protected] scripts]# ./b.sh
in a-----hahaha
in b-----

 这样子呢：不可以啊，因为b调a，b是父。a是子，a定义export，只是让a的子进程有用

[[email protected] scripts]# cat a.sh
#!/bin/bash
export a=hahaha
echo "in a-----"$a
[[email protected] scripts]# cat b.sh
#!/bin/bash
./a.sh
echo "in b-----"$a
[[email protected] scripts]# ./b.sh
in a-----hahaha
in b-----

 应该这样

[[email protected] scripts]# cat a.sh
#!/bin/bash
export a=hahaha
echo "in a-----"$a
./b.sh
[[email protected] scripts]# cat b.sh
#!/bin/bash
echo "in b-----"$a
[[email protected] scripts]# ./a.sh
in a-----hahaha
in b-----hahaha

 结论：export  A   #可把变量提升为当前shell进程中的全局环境变量，可供其他子shell程序使用

或者：source 的意思是使 b.sh 也在 a.sh 的进程里面

[[email protected] scripts]# cat a.sh
#!/bin/bash
a=hahaha
echo "in a-----"$a
source /home/xiaofeng/scripts/b.sh
[[email protected] scripts]# cat b.sh
#!/bin/bash
echo "in b-----"$a
[[email protected] scripts]# ./a.sh
in a-----hahaha
in b-----hahaha

 注意：source 也可以用“.”代替

. /home/xiaofeng/scripts/b.sh

将命令值赋予给一个变量，反引号：``

[[email protected] scripts]# ll
total 12
-rwxr-xr-x. 1 root root 75 Jul 29 20:05 a.sh
-rwxr-xr-x. 1 root root 31 Jul 28 15:08 b.sh
-rwxr-xr-x. 1 root root 32 Jul 28 14:24 helloworld.sh
[[email protected] scripts]# a=`ll`
[[email protected] scripts]# echo $a
total 12 -rwxr-xr-x. 1 root root 75 Jul 29 20:05 a.sh -rwxr-xr-x. 1 root root 31 Jul 28 15:08 b.sh -rwxr-xr-x. 1 root root 32 Jul 28 14:24 helloworld.sh
[[email protected] scripts]# a=`date`
[[email protected] scripts]# echo $a
Sun Jul 29 20:14:40 CST 2018
[[email protected] scripts]# 

 或者美元加括号

[[email protected] scripts]# a=$(date)
[[email protected] scripts]# echo $a
Sun Jul 29 20:16:38 CST 2018

4、特殊变量

$? 表示上一个命令退出的状态码

$$ 表示当前进程编号

$0 表示当前脚本名称

$n 表示n位置的输入参数（n代表数字，n>=1）

$# 表示参数的个数，常用于循环

$*和[email protected] 都表示参数列表 

[[email protected] scripts]# date
Sun Jul 29 20:18:55 CST 2018
[[email protected] scripts]# echo $?
0
[[email protected] scripts]# ad
-bash: ad: command not found
[[email protected] scripts]# echo $?
127
[[email protected] scripts]# true
[[email protected] scripts]# echo $?
0
[[email protected] scripts]# false
[[email protected] scripts]# echo $?
1

 $n

[[email protected] scripts]# cat c.sh
echo $1 $2 $3
[[email protected] scripts]# ./c.sh aaa bbb ccc
aaa bbb ccc

 

 

 

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