我知道 bash 有一个>>
运算符,将输出附加到文件,但是该运算符有什么用呢<<
?
答案1
使用
info bash
然后搜索(输入 '/' 然后输入 '<<')。
以下是部分引文:
Here Documents
This type of redirection instructs the shell to read input from the
current source until a line containing only delimiter (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 characters 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, com‐
mand substitution, and arithmetic expansion. In the latter case, the
character sequence \<newline> is ignored, and \ must be used to quote
the characters \, $, and `.
If the redirection operator is <<-, then all leading tab characters are
stripped from input lines and the line containing delimiter. This
allows here-documents within shell scripts to be indented in a natural
fashion.
Here Strings
A variant of here documents, the format is:
<<<word
The word is expanded and supplied to the command on its standard input. [...]
答案2
$ cat <<EOF
> This is a test
> EOF
This is a test
$