我尝试使用FIFO做一些简单的事情:读取行,但不是一次性读取,结果意外地“没有起作用”。
这是可以的:
我仍然不理解中间的情景。有人能解释一下吗?
这是可以的:
$ f=$(mktemp -u)
$ mkfifo $f
$ { seq 5 > $f; } &
[1] 2486
$ while read line; do echo $line; done < $f
1
2
3
4
5
[1]+ Done { seq 10 > $f; }
但是如果我逐行阅读,第一次读取成功,而第二次读取则会挂起。
$ { seq 5 > $f; } &
[1] 2527
$ read line < $f; echo $line
1
[1]+ Done { seq 5 > $f; }
$ read line < $f; echo $line
[hangs here...]
有人能解释一下吗?为什么我不能逐行阅读所有5行?剩下的数据发生了什么事?
我发现如果我创建一个文件描述符来重定向FIFO,就可以逐行阅读:
$ { seq 5 > $f; } &
[1] 2732
$ exec 3<$f
[1]+ Done { seq 5 > $f; }
$ read -u 3 line && echo $line || echo no more data
1
$ read -u 3 line && echo $line || echo no more data
2
$ read -u 3 line && echo $line || echo no more data
3
$ read -u 3 line && echo $line || echo no more data
4
$ read -u 3 line && echo $line || echo no more data
5
$ read -u 3 line && echo $line || echo no more data
no more data
$ exec 3<&-
我仍然不理解中间的情景。有人能解释一下吗?
版本信息:
$ bash --version
GNU bash, version 4.2.25(1)-release (i686-pc-linux-gnu)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ mkfifo --version
mkfifo (GNU coreutils) 8.13
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by David MacKenzie.
GNU bash,版本4.2.25(1)-release(x86_64-pc-linux-gnu)
- devnull