Shell 编程 基础

本篇主要写一些shell脚本的基础知识，编程规范。

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第一个shell脚本

[root@localhost ~]# vim first.sh

#!/bin/bash
# this is first shell script !
cd /boot/
echo "当前所在路径："
pwd
echo "以vml为开头的文件信息："
ls -lh vml*

执行脚本

source

[root@localhost ~]# source first.sh 
当前所在路径：
/boot
以vml为开头的文件信息：
-rwxr-xr-x. 1 root root 5.7m sep  4 14:02 vmlinuz-0-rescue-ec132d04a74d4b7e828b3905a6b83437
-rwxr-xr-x. 1 root root 5.7m aug 23  2017 vmlinuz-3.10.0-693.el7.x86_64
[root@localhost boot]# 

.

[root@localhost ~]# . first.sh 
当前所在路径：
/boot
以vml为开头的文件信息：
-rwxr-xr-x. 1 root root 5.7m sep  4 14:02 vmlinuz-0-rescue-ec132d04a74d4b7e828b3905a6b83437
-rwxr-xr-x. 1 root root 5.7m aug 23  2017 vmlinuz-3.10.0-693.el7.x86_64
[root@localhost boot]# 

sh

[root@localhost ~]# sh first.sh 
当前所在路径：
/boot
以vml为开头的文件信息：
-rwxr-xr-x. 1 root root 5.7m sep  4 14:02 vmlinuz-0-rescue-ec132d04a74d4b7e828b3905a6b83437
-rwxr-xr-x. 1 root root 5.7m aug 23  2017 vmlinuz-3.10.0-693.el7.x86_64
[root@localhost ~]# 

./

[root@localhost ~]# ./first.sh
bash: ./first.sh: permission denied
[root@localhost ~]# ls -lh first.sh 
-rw-r--r--. 1 root root 139 sep 23 22:04 first.sh
[root@localhost ~]# chmod +x first.sh 
[root@localhost ~]# ls -lh first.sh 
-rwxr-xr-x. 1 root root 139 sep 23 22:04 first.sh
[root@localhost ~]# ./first.sh 
当前所在路径：
/boot
以vml为开头的文件信息：
-rwxr-xr-x. 1 root root 5.7m sep  4 14:02 vmlinuz-0-rescue-ec132d04a74d4b7e828b3905a6b83437
-rwxr-xr-x. 1 root root 5.7m aug 23  2017 vmlinuz-3.10.0-693.el7.x86_64

符号使用

管道符 和 awk

[root@localhost ~]# grep "/bin/bash$" /etc/passwd | awk -f: '{print $1,$7}'
root /bin/bash

[root@localhost ~]# grep "/bin/bash$" /etc/passwd | awk -f":" '{print $1,$7}'
root /bin/bash

[root@localhost ~]# df -ht | grep "/$" | awk '{print $1,$6}'
/dev/sda2 21%

[root@localhost ~]# df -ht | grep "/$" | awk -f" " '{print $1,$6}'
/dev/sda2 21%

重定向输出

[root@localhost ~]# echo "123" > test.txt
[root@localhost ~]# cat test.txt 
123

[root@localhost ~]# echo "456" >> test.txt 
[root@localhost ~]# cat test.txt 
123
456

重定向输入

[root@localhost ~]# rm test.txt 
rm: remove regular file ‘test.txt’? ^c

[root@localhost ~]# echo "y" > temp.txt
[root@localhost ~]# ls te*
temp.txt  test.txt

[root@localhost ~]# rm test.txt < temp.txt 
rm: remove regular file ‘test.txt’? [root@localhost ~]# 
[root@localhost ~]# ls te*
temp.txt

错误重定向

• 混合输出

[root@localhost ~]# tar zcvf opt.tar.gz /opt/ &> error.log 
[root@localhost ~]# cat error.log 
tar: removing leading `/' from member names
/opt/
/opt/rh/

• 标准错误输出

[root@localhost ~]# tar zcvf opt.tar.gz /opt/ 2> error.log 
/opt/
/opt/rh/
[root@localhost ~]# cat error.log 
tar: removing leading `/' from member names

[root@localhost ~]# tar zcvf opt.tar.gz /opt/ 2>> error.log 
/opt/
/opt/rh/
[root@localhost ~]# cat error.log 
tar: removing leading `/' from member names
tar: removing leading `/' from member names

变量

定义、查看变量

[root@localhost ~]# product=java
[root@localhost ~]# version=1.8
[root@localhost ~]# echo $product 
java
[root@localhost ~]# echo $product $version 
java 1.8

大括号

[root@localhost ~]# echo $product1.8
.8
[root@localhost ~]# echo ${product}1.8
java1.8

引号

[root@localhost ~]# echo "java $version"
java 1.8
[root@localhost ~]# echo 'java $version'
java $version

反撇号

[root@localhost ~]# which cat
/usr/bin/cat
[root@localhost ~]# ls -lh /usr/bin/cat
-rwxr-xr-x. 1 root root 53k nov  6  2016 /usr/bin/cat
[root@localhost ~]# ls -lh `which cat`
-rwxr-xr-x. 1 root root 53k nov  6  2016 /usr/bin/cat

read

[root@localhost ~]# read -p "请输入一个整数：" num
请输入一个整数：10
[root@localhost ~]# echo $num 
10

变量作用范围

• 设置局部变量为全局变量

[root@localhost ~]# echo $product $version 
java 1.8
[root@localhost ~]# bash
[root@localhost ~]# echo $product $version

[root@localhost ~]# exit
[root@localhost ~]# export product version
[root@localhost ~]# bash
[root@localhost ~]# echo $product $version
java 1.8

• 直接定义全局变量

[root@localhost ~]# export num=100
[root@localhost ~]# echo $num
100
[root@localhost ~]# bash
[root@localhost ~]# echo $num 
100

数值变量的运算

[root@localhost ~]# num1=8
[root@localhost ~]# num2=5
[root@localhost ~]# expr $num1 + $num2
13
[root@localhost ~]# expr $num1 - $num2
3
[root@localhost ~]# expr $num1 \* $num2
40
[root@localhost ~]# expr $num1 / $num2
1
[root@localhost ~]# expr $num1 % $num2
3

• demo

[root@localhost ~]# vim suanshu.sh

#!/bin/bash
read -p "请输入第1个数字：" num1
read -p "请输入第2个数字：" num2
result1=`expr $num1 + $num2`
result2=`expr $num1 - $num2`
result3=`expr $num1 \* $num2`
result4=`expr $num1 / $num2`
result5=`expr $num1 % $num2`
echo "加法：$num1 + $num2 = $result1"
echo "减法：$num1 - $num2 = $result2"
echo "乘法：$num1 * $num2 = $result3"
echo "除法：$num1 / $num2 = $result4"
echo "取余：$num1 % $num2 = $result5"

[root@localhost ~]# chmod +x suanshu.sh 
[root@localhost ~]# ./suanshu.sh 
请输入第1个数字：8
请输入第2个数字：5
加法：8 + 5 = 13
减法：8 - 5 = 3
乘法：8 * 5 = 40
除法：8 / 5 = 1
取余：8 % 5 = 3

特殊变量

环境变量

[root@localhost ~]# env

位置变量

[root@localhost ~]# vim suanshu.sh

#!/bin/bash
echo "第一个位置变量值为：$1"
echo "第二个位置变量值为：$2"
result1=`expr $1 + $2`
result2=`expr $1 - $2`
result3=`expr $1 \* $2`
result4=`expr $1 / $2`
result5=`expr $1 % $2`
echo "加法：$1 + $2 = $result1"
echo "减法：$1 - $2 = $result2"
echo "乘法：$1 * $2 = $result3"
echo "除法：$1 / $2 = $result4"
echo "取余：$1 % $2 = $result5"

[root@localhost ~]# chmod +x suanshu.sh 
[root@localhost ~]# ./suanshu.sh 8 5
第一个位置变量值为：8
第二个位置变量值为：5
加法：8 + 5 = 13
减法：8 - 5 = 3
乘法：8 * 5 = 40
除法：8 / 5 = 1
取余：8 % 5 = 3

预定义变量

[root@localhost ~]# vim suanshu.sh

#!/bin/bash
echo "第一个位置变量值为：$1"
echo "第二个位置变量值为：$2"
result1=`expr $1 + $2`
result2=`expr $1 - $2`
result3=`expr $1 \* $2`
result4=`expr $1 / $2`
result5=`expr $1 % $2`
echo "加法：$1 + $2 = $result1"
echo "减法：$1 - $2 = $result2"
echo "乘法：$1 * $2 = $result3"
echo "除法：$1 / $2 = $result4"
echo "取余：$1 % $2 = $result5"
echo "执行的脚本名称：$0"
echo "执行的参数个数：$#"
echo "执行的参数内容：$*"

[root@localhost ~]# chmod +x suanshu.sh 
[root@localhost ~]# ./suanshu.sh 8 5
第一个位置变量值为：8
第二个位置变量值为：5
加法：8 + 5 = 13
减法：8 - 5 = 3
乘法：8 * 5 = 40
除法：8 / 5 = 1
取余：8 % 5 = 3
执行的脚本名称：./suanshu.sh
执行的参数个数：2
执行的参数内容：8 5
[root@localhost ~]# echo $?
0