shell脚本汇总

## 解析地址中的域名

```bash
#!/bin/bash

echo parse doamin in full url

full_url=http://www.baidu.com/aaaa/bbb/ccc
echo ${full_url}
first_index_with_prefix=`expr index ${full_url} "://"`
first_index=`expr ${first_index_with_prefix} + 3`
url_without_schema=$(expr substr ${full_url} ${first_index} ${#full_url})
echo url_without_schema=${url_without_schema}
next_index_with_prefix=`expr index ${url_without_schema} "/"`
if [ 0 == ${next_index_with_prefix} ]; then
    domain_in_url=${url_without_schema}
else
    next_index=`expr ${next_index_with_prefix} - 1`
    echo next_index=${next_index}
    domain_in_url=$(expr substr ${url_without_schema} 1 ${next_index})
fi

echo domain_in_url=${domain_in_url}
```

## 一行一行读取文件内容

用于将jar包列表保存到文件中，再读取出的情况。

```bash
# $filename文件最后要有一个空行，不然最后一条数据获取不了
while read LINE
do
    echo $LINE
done < $filename
```

## shell示例

```bash
#!/bin/bash

echo start on $(date "+%Y-%m-%d %H:%M:%S")

shell_directory=$(cd `dirname $0`; pwd)
echo "shell directory is $shell_directory"
echo "filename is $0"

echo "argument number is $#"

if [ $# -lt 1 ]
        then
                echo "argument num should not be less than one"
                exit
fi

if [ $1 == "start" ]
        then
                echo do_start
elif [ $1 == "stop" ]
        then
                echo do_stop
else
        echo "wrong argument!"
fi
```

## centos7中安装指定版本的python3

```bash
#!/bin/bash

# 若不需要指定版本可以执行如下命令
# sudo yum install -y python3

# see https://www.cnblogs.com/xiujin/p/11477419.html
sudo yum -y groupinstall "Development tools"
sudo yum -y install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gdbm-devel db4-devel libpcap-devel xz-devel
sudo yum install -y libffi-devel zlib1g-dev
sudo yum install zlib* -y
# wget https://www.python.org/ftp/python/3.7.2/Python-3.7.2.tar.xz
wget https://repo.huaweicloud.com/python/3.7.2/Python-3.7.2.tar.xz
tar -xvJf  Python-3.7.2.tar.xz
sudo mkdir /usr/local/python3
cd Python-3.7.2
# 好像脚本不完整。
# 安装后不用配置环境变量，使用全路径即可，如/usr/local/python3/python
```

## 获取cpu数量

```
# 可以把内容放到.bashrc中，然后执行cpu_count就可以
function cpu_count() {
  grep -c ^processor /proc/cpuinfo
}
```