将行重定向到shell中for循环下的不同文件

I want to put certain lines in to two different files in a shell script. How should I put the syntax for this.

我想在shell脚本中将某些行放入两个不同的文件中。我该怎么做这个的语法。

Example:

A for loop prints 6 lines, and I want that the first two lines should be appended to 1st file, and the last 4 lines should be appended to the other file.

for循环打印6行,我希望前两行应该附加到第一个文件,最后4行应该附加到另一个文件。

2 个解决方案

#1

A for loop prints 6 lines, and I want that the first two lines should be appended to 1st file, and the last 4 lines should be appended to the other file.

for循环打印6行,我希望前两行应该附加到第一个文件,最后4行应该附加到另一个文件。

There is no way. One option would be to redirect everything to a file and then copy the desired sections of the log to other files.

没有办法。一种选择是将所有内容重定向到文件,然后将日志的所需部分复制到其他文件。

for i in {1..6}; do
  echo $i > log
done

head -4 log >> logfile1  # Appends the first four lines to logfile1
tail -2 log >> logfile2  # Appends the last two lines to logfile2

#2

Answer

If you're using BASH you can use tee to send the same input to both head -n2 and tail -n4 at the same time using a combination of process substitution and a pipe:

如果你正在使用BASH,你可以使用tee使用进程替换和管道的组合同时向head -n2和tail -n4发送相同的输入:

$ for i in {1..6}; do echo $i; done | tee >(head -n2 >first2.txt) | tail -n4 >last4.txt
$ cat first2.txt
1
2
$ cat last4.txt
3
4
5
6

Explanation

By default tee takes its STDIN and copies it to file(s) specified as arguments in addition to its STDOUT. Since process substitution returns a /dev/fd path to a file descriptor (echo >(true) to see an example) tee is able to write to that path like any other regular file.

默认情况下,除了STDOUT之外,tee还会将其STDIN复制到指定为参数的文件中。由于进程替换将/ dev / fd路径返回到文件描述符(echo>(true)以查看示例),因此tee能够像任何其他常规文件一样写入该路径。

Here's what the tee command looks like after substitution:

以下是替换后tee命令的样子:

tee /dev/fd/xx | tail -n4 >last4.txt

Or more visually:

或者更直观:

tee | tail -n4 >last4.txt
 :
 /dev/fd/xx
 :
 :..>(head -n2 >first2.txt)

So the output gets copied both to the head process (Whose output is redirected to first2.txt) and out STDIN which is piped to the tail process:

因此输出被复制到head进程(其输出重定向到first2.txt)和输出到尾进程的STDIN:

Note that process substitution is a BASH-ism, so if you're using a different shell or concerned about POSIX compliance it might not be available.

请注意,进程替换是BASH-ism,因此如果您使用的是其他shell或者关注POSIX兼容性,则可能无法使用它。