我最近在 bash 中遇到了这个命令:
cat > filename << EOF
我不明白这<< EOF
部分。谷歌搜索<<
运算符,我只遇到了常规的左移算术。玩弄它也没有给我任何洞察力。
任何解释将不胜感激!
答案1
它的here document
描述如下man bash
:
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 and variable 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-docu- ment are not expanded. If word is unquoted, all
lines of the here-document are subjected to parameter
expansion, command substitution, and arithmetic expansion, the
character sequence \<newline> is ignored, and \ must be used to
quote the char- acters \, $, 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.
用法示例:
$ cat > filename << EOF
> Write this line to filename
> And this line
> And this
> EOF
$ cat filename
Write this line to filename
And this line
And this