为什么 bzip2 --version 表现得很奇怪？

Question

所以如果我输入命令

$ gzip --version | head -n1

一切都按预期进行。但是如果我用 bzip2 尝试同样的方法：

$ bzip2 --version | head -n1

我有很多行，我必须按Ctrl-C终止。

这里发生了什么？

编辑：

被打印的行

$ bzip2 --version | head -n1

bzip2, a block-sorting file compressor.  Version 1.0.6, 6-Sept-2010.

Copyright (C) 1996-2010 by Julian Seward.

This program is free software; you can redistribute it and/or modify
it under the terms set out in the LICENSE file, which is included
in the bzip2-1.0.6 source distribution.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
LICENSE file for more details.

我必须按Ctrl-C继续。

如果我省略管道我得到

$ bzip2 --version 

bzip2, a block-sorting file compressor.  Version 1.0.6, 6-Sept-2010.

Copyright (C) 1996-2010 by Julian Seward.

This program is free software; you can redistribute it and/or modify
it under the terms set out in the LICENSE file, which is included
in the bzip2-1.0.6 source distribution.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
LICENSE file for more details.

bzip2: I won't write compressed data to a terminal.
bzip2: For help, type: `bzip2 --help'.

如果我将 stdout 与 stderr 合并为 @devnull sais，它会很好地显示行，但我需要按Ctrl- C。我试过

$ gcc 2>&1 | head -n1

它运行良好，所以我认为bzip2命令中仍然缺少一些东西。

编辑2：

我用以下命令解决了这个问题：

$ bzip2 --version 2>&1 < /dev/null | head -n1 

但我还是不明白问题所在。

Answer 1

不同之处在于gzip --version输出到STDOUT而bzip2 --version输出到STDERR。

合并STDERR到STDOUT你会看到预期的：

$ bzip2 --version 2>&1 | head -n1
bzip2, a block-sorting file compressor.  Version 1.0.6, 6-Sept-2010.