Linux Bash编程：shell语法及实用技巧
在Linux Bash编程中，介绍了Bash编程基本语法，本文记录一下Bash编程中使用到的相关shell 语法技巧。
目录
字符串处理
在字符串中传递变量
$ num=8
# 方法1：双引号
$ text="There are $num ducks swimming in a pond"
$ echo $text
There are 8 ducks swimming in a pond
$
$ text="There are "$num" ducks swimming in a pond"
$ echo $text
There are 8 ducks swimming in a pond
# 方法2：单引号
$ text='There are $num ducks swimming in a pond'
$ echo $text
There are $num ducks swimming in a pond
$
$ text='There are '$num' ducks swimming in a pond'
$ echo $text
There are 8 ducks swimming in a pond
$ text="There are '$num' ducks swimming in a pond"
$ echo $text
There are '8' ducks swimming in a pond
tr命令
tr (translate) 命令用于删除或者转换字符，比如大小写转换，删除字符等。命令格式如下：
$ tr [OPTION] SET1 [SET2]
OPTION参数说明：
-c | --complement：删除或者替换SET1以外的字符-d | --delete：删除SET1以外的字符-s, --squeeze-repeats：压缩连续重复的字符为单个字符-t, --truncate-set1：截取 SET1 使之与 SET2 长度相等
1. 大小写转换
$ echo HELLO WORLD | tr "A-Z" "a-z"
hello world
$ echo HELLO WORLD | tr "[:upper:]" "[:lower:]"
hello world
$
$ echo hello world | tr "a-z" "A-Z"
HELLO WORLD
$ echo hello world | tr "[:lower:]" "[:upper:]"
HELLO WORLD
2. 替换
$ echo "(hello world)" | tr "()" "{}"
{hello world}
3. 压缩重复字符串
比如可以将多个连续空格压缩为一个空格
$ echo "hello world !" | tr -s [:space:] ' '
hello world !
4. 删除指定字符
$ echo "10MB" | tr -d MB
10
提取数字还可以这样：
$ echo "10MB" | tr -cd "[0-9]"
10
$ echo "10MB" | tr -cd [:digit:]
10
删除数字：
$ echo "10MB" | tr -d "[0-9]"
MB
$ echo "10MB" | tr -d [:digit:]
MB
字母字符用[:alpha:]表示
判断字符串是否包含某个子串
1、使用通配符*
SIZE=10M
if [[ $SIZE == *M* ]]
then
echo "$SIZE include M"
fi
2、使用操作符~
if [[ $SIZE =~ M ]]
then
echo "$SIZE include M"
fi
3、利用grep查找
SIZE=10Mb
result=`echo $SIZE | grep "Mb"`
if [ "$result" != "" ]
then
echo "$SIZE include Mb"
fi
4、利用grep查找，不区分大小写
SIZE=10Mb
result=`echo $SIZE | grep -i "mb"`
if [ "$result" != "" ]
then
echo "The units are correct"
fi
数组操作
冒泡排序
#!/bin/bash
BubbleSort()
{
# 冒泡排序
# Performing Bubble sort
num_length=${#arry[*]}
for (( i = 0; i<$num_length; i++ ))
do
for (( j = 0; j<$num_length-i-1; j++ ))
do
if [[ ${arry[j]} -gt ${arry[$(( j+1 ))]} ]]
then
# swap
temp=${arry[j]}
arry[$j]=${arry[$((j+1))]}
arry[$(( j+1 ))]=$temp
fi
done
done
echo "Array in sorted order :"
echo -e "\E[1;31m${arry[*]} \033[0m"
}
arry=(9 8 5 6 2 4 7 1)
BubbleSort
字体颜色
常用颜色格式：
normal='\033[0m' # 默认颜色
style='\033[1m' # 高亮
style='\033[4m' # 添加下划线
style='\033[7m' # 反显
color='\033[32m' # 绿色字体
color='\033[30m' # 黑色
color='\033[31m' # 红色
color='\033[33m' # 黄色
color='\033[34m' # 蓝色
color='\033[35m' # 紫色
color='\033[36m' # 深绿
color='\033[37m' # 白色
使用方法：
echo -e "\033[1m" "There are 8 ducks swimming in a pond"
echo -e "\033[0m" "There are 8 ducks swimming in a pond"
echo -e "\033[4m" "There are 8 ducks swimming in a pond"
echo -e "\033[7m" "There are 8 ducks swimming in a pond"
echo -e "\033[32m" "There are 8 ducks swimming in a pond"
文本处理
文件操作
sed -i '/^$/d' test.txt # 删除空行
sed -i 's/ *//g' test.txt # 删除空格
IFS=$'\n' # linux分隔符，默认是空格
for lines in `cat test.txt`; do # 循环读取每一行
pic=`echo $lines | grep '\!\[\]('` # 处理读取的内容：使用Linux三剑客进行文本处理
if [ "$pic" != "" ]
then
echo $pic >> new_file.txt
fi
# do something
done
清空文件内容
用于每次写文件时清空文件内容，下面介绍5种方法，前面4种方法中，如果文件不存在会创建文件。
$ cat /dev/null > test.txt
$ : > test.txt
$ > test.txt
$ true > test.txt
$ sed -i '1,$d' test.txt # 如果文件test.txt不存在会报错
欢迎关注公众号:「测试开发小记」及时接收最新技术文章！
