Question

我在git网站上看到了这个：

mkdir log
echo '*.log' > log/.gitignore
git add log
echo tmp >> .gitignore
git add .gitignore
git commit -m "ignored log files and tmp dir"

因此，在echo的第一个实例中，我们将字符串写入日志目录中的文件.gitignore。在第二个例子中，我们是否将tmp写入文件.gitignore（在当前目录中）。为什么我们需要使用＆gt;＆gt;与＆gt; ？

Answer 1

当向文件回显某些内容时，>会附加到该文件，而➜ ~ echo foobar > test ➜ ~ cat test foobar ➜ ~ echo baz >> test ➜ ~ cat test foobar baz ➜ ~ echo foobar > test ➜ ~ cat test foobar会覆盖该文件。

*.log

从您发布的示例中，创建了一个日志目录，然后将log/.gitignore放入>，以便不会将任何日志文件提交给git。由于使用了*.log，如果存在.gitignore文件，则只会覆盖>>。

然后将日志目录本身添加到本地git阶段。

在下一行中，添加了tmp，以便将_stack()附加到.gitignore文件的末尾，而不是覆盖它。然后将其添加到暂存区域。

Answer 2

>是一个重定向运算符。 < > >| << >> <& >& <<- <>是shell命令解释器中的所有重定向运算符。

在您的示例中，基本上>覆盖并>>追加。

请参阅man sh，（您的终端可以通过man sh访问手册。）

Redirections
     Redirections are used to change where a command reads its input or sends its output.  In
     general, redirections open, close, or duplicate an existing reference to a file.  The over‐
     all format used for redirection is:

           [n] redir-op file

     where redir-op is one of the redirection operators mentioned previously.  Following is a
     list of the possible redirections.  The [n] is an optional number, as in '3' (not '[3]'),
     that refers to a file descriptor.

           [n]> file   Redirect standard output (or n) to file.

           [n]>| file  Same, but override the -C option.

           [n]>> file  Append standard output (or n) to file.

           [n]< file   Redirect standard input (or n) from file.

           [n1]<&n2    Duplicate standard input (or n1) from file descriptor n2.

           [n]<&-      Close standard input (or n).

           [n1]>&n2    Duplicate standard output (or n1) to n2.

           [n]>&-      Close standard output (or n).

           [n]<> file  Open file for reading and writing on standard input (or n).

     The following redirection is often called a "here-document".

           [n]<< delimiter
                 here-doc-text ...
           delimiter

     All the text on successive lines up to the delimiter is saved away and made available to the
     command on standard input, or file descriptor n if it is specified.  If the delimiter as
     specified on the initial line is quoted, then the here-doc-text is treated literally, other‐
     wise the text is subjected to parameter expansion, command substitution, and arithmetic
     expansion (as described in the section on "Expansions").  If the operator is "<<-" instead
     of "<<", then leading tabs in the here-doc-text are stripped.

使用echo; ＆gt;有什么区别？和＆gt;＆gt;

2 个答案: