This type of redirection instructs the shell to read input from the urrent source
until a line containing only word (with no trailing blanks) is seen.
All of the lines read up to that point are then used as the standard input for a command.
The format of here-documents is:
<<[-]word
here-document
delimiter
No parameter expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word. If any charac-
ters in word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not
expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and
arithmetic expansion. In the latter case, the character sequence \<newline> is ignored, and \ must be used to quote the charac-
ters \, $, and `.
If the redirection operator is <<-, then all leading tab characters are stripped from input lines and the line containing delim-
iter. This allows here-documents within shell scripts to be indented in a natural fashion.
以上是 man
EOF多行写入文件防止变量替换 问题描述# 对多个变量及多行输出到文件，存在变量自动替换，当使用cat«EOF不想对内容进行变量替换、命令替换、参数展开等
问题解决# 转义特殊字符如 $ `等
一、对 $·\ 进行转义
cat >> a.sh << EOF
echo \`hostname\`
echo $HOME
EOF
二、在分界符EOF前添加反斜杠\，或者用单引号、双引号括起来
cat >> a.sh << \EOF
echo `hostname`
echo $HOME
EOF
cat >> a.sh << "EOF"
echo `hostname`
echo $HOME
EOF
cat >> a.sh << 'EOF'
echo `hostname`
echo $HOME
EOF
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