bash 管道传递的多行语法；这是便携的吗？
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Multiline syntax for piping a heredoc; is this portable?
提问by William Pursell
I'm familiar with this syntax:
我熟悉这种语法：
cmd1 << EOF | cmd2
text
EOF
but just discovered that bash allows me to write:
但刚刚发现 bash 允许我写：
cmd1 << EOF |
text
EOF
cmd2
(the heredoc is used as input to cmd1, and the output of cmd1 is piped to cmd2). This seems like a very odd syntax. Is it portable?
（heredoc 用作 cmd1 的输入，cmd1 的输出通过管道传输到 cmd2）。这似乎是一个非常奇怪的语法。便携吗？
采纳答案by Ned Deily
Yes, the POSIX standard allows this. According to the 2008 version:
是的，POSIX 标准允许这样做。 根据 2008 版：
The here-document shall be treated as a single word that begins after the next
<newline>and continues until there is a line containing only the delimiter and a<newline>, with no<blank>characters in between. Then the next here-document starts, if there is one.
here-document 应被视为一个单词，它在下一个之后开始
<newline>，一直持续到有一行只包含分隔符和 a<newline>，中间没有<blank>字符。然后下一个 here-document 开始，如果有的话。
And includes this example of multiple "here-documents" in the same line:
并在同一行中包含多个“此处文档”的示例：
cat <<eof1; cat <<eof2
Hi,
eof1
Helene.
eof2
So there is no problem doing redirections or pipes. Your example is similar to something like this:
所以做重定向或管道没有问题。您的示例类似于以下内容：
cat file |
cmd
And the shell grammar (further down on the linked page) includes these definitions:
shell 语法（在链接页面的下方）包括以下定义：
pipe_sequence : command
| pipe_sequence '|' linebreak command
newline_list : NEWLINE
| newline_list NEWLINE
;
linebreak : newline_list
| /* empty */
So a pipe symbol can be followed by an end-of-line and still be considered part of a pipeline.
所以管道符号后面可以跟一个行尾，并且仍然被认为是管道的一部分。
回答by Jens
Yes it's in the POSIX shell grammar. You can also have more than one here-doc for the same command(some other examples use two catinvocations, but this works as well):
是的，它在 POSIX shell 语法中。对于同一个命令，您还可以有多个 here-doc（其他一些示例使用两个cat调用，但这也适用）：
cat <<EOF1 <<EOF2
first here-doc
EOF1
second here-doc
EOF2
This is contrived (using 2 here-docs for stdin), but if you think of providing input for different file descriptors it immediately makes sense.
这是人为的（将 2 个 here-docs 用于标准输入），但是如果您考虑为不同的文件描述符提供输入，它立即就有意义了。
There's also the possibility to drop the catentirely. Why not make the here-document directly available to cmd:
也有可能完全删除cat. 为什么不直接将 here-document 提供给cmd：
cmd << EOF
input
here
EOF
回答by TMS
Hmm, I suppose yes, according to the test in bash in POSIX mode:
嗯，我想是的，根据 bash 在 POSIX 模式下的测试：
$ bash --posix
$ cat <<EOF |
> ahoj
> nazdar
> EOF
> sed 's/a/b/'
bhoj
nbzdar
回答by buc
Hi, check this, for example
嗨，检查这个，例如
#!/bin/sh
( base32 -d | base64 -d )<<ENDOFTEXT
KNDWW42DNNSHS5ZXPJCG4MSVM5MVQVT2JFCTK3DELBFDCY2IIJYGE2JUJNHWS22LINVHQMCMNVFD
CWJQIIZVUV2JOVNEOVJLINTW6PIK
ENDOFTEXT
regards
问候
