shell及正则相关知识点

前向搜索
?=和?!
后向搜索
?<=和?<!

# how to print the web cotent to the console without donwload it.
wget -q -O - http://www.baidu.com/
# with post data
wget -q -O - http://www.baidu.com/ --post-data=imgContinue=Continue+to+image+...+

# or you can use curl
curl http://www.baidu.com/ -d imgContinue=Continue+to+image+...+

# grep something, sometimes you have to grep two times
grep -o "http://www.baidu.com/.*.jpg' title" | grep -o http.*jpg

wget 指定下载目录
wget -P

匹配base64编码

64.txt内容
<img src="data:image/png;base64,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" alt="">
grep -o '<img src="data:image/png;base64,[0-9a-zA-Z+/=]*" alt=""' 64.txt