linux - shell命令求解

问题描述

问 题

先贴命令

cat >> /etc/ssh/sshd_config << 'EOF'
KexAlgorithms diffie-hellman-group1-sha1,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group1-sha1,[e-mail]
EOF

cat我知道是查看文件的意思，可是这条>> 和 << 是什么意思呢，求教

还有一句：

/bin/sed -i 's/#Banner/Banner/' /etc/ssh/sshd_config

求解命令

解决方案

第一条命令：
cat >> /etc/ssh/sshd_config << 'EOF'

1. >> filename：标准输出重定向，在此处意思是将标准输出重定向到写入到后面的filename（默认是直接输出到终端），和>不同的是，会seed到文件结束位置，再写入，相当于append文件。

2. << token inputs：标准输入重定向，意思加后面的inputs重定向为标准输入，直到匹配到token结束。

表达能力有限，直接看下面吧

< file means open a file for reading and associate with STDIN. 
<< token Means use the current input stream as STDIN for the program until token is seen. We will ignore this one until we get to scripting. 
> file means open a file for writing and truncate it and associate it with STDOUT. 
>> file means open a file for writing and seek to the end and associate it with STDOUT. This is how you append to a file using a redirect. 
n>&m means redirect FD n to the same places as FD m. Eg, 2>&1 means send STDERR to the same place that STDOUT is going to. 

第二条命令：
/bin/sed -i 's/#Banner/Banner/' /etc/ssh/sshd_config

sed -i 's/search/replace' file：在文件file，搜索到search替换为replace。

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