为什么备用分隔符不适用于 sed -e '/pattern/s/a/b/'? [英] Why do alternate delimiters not work with sed -e '/pattern/s/a/b/'?

问题描述

这里有一些我发现没有意义的东西.

Here is something I have discover that doesn't make sense.

cat config.h 的输出:

define somevar foo // Sample variable

此版本的命令用于将 foo 更改为 bar 并保留注释:

This version of the command works to change foo to bar and preserve the comments:

sed -e '/somevar/s/foo/bar/' config.h

这不起作用:

sed -e '|somevar|s|foo|bar|' config.h

出现此错误:

sed:-e 表达式 #1，字符 1:未知命令:`|'

sed: -e expression #1, char 1: unknown command: `|'

有趣的是，这确实有效:

Funnily enough this does work:

sed -e '/somevar/s|foo|bar|' config.h

也许我遗漏了文档的某些部分.在同一个 sed 命令中使用两个不同的分隔符似乎很奇怪.

Perhaps I am missing some part of the documentation. It seems very odd to have two different delimiters in the same sed command.

错误或功能?

推荐答案

这会起作用:

sed -e '\|somevar|s|foo|bar|'

GNU sed 的 man 页面对此非常清楚:

The man page of GNU sed is pretty clear about this:

   /regexp/
          Match lines matching the regular expression regexp.

   \cregexpc
          Match lines matching the regular expression regexp.  The  c  may
          be any character.

即c可以是任意字符，但\是必须的.

That is, the c may be any character, but the starting \ is mandatory.

我周围没有 FreeBSD，但根据 @bonsaivikingman页面里面也很清楚:

I don't have a FreeBSD around, but according to @bonsaiviking the man page there is also very clear:

开头分隔符前面需要有反斜杠，除非它是斜杠.

The opening delimiter needs to be preceded by a backslash unless it is a slash.

另一方面，在 OSX 中，这一点都不清楚:

On the other hand in OSX this is not clear at all:

      In a context address, any character other than a backslash (``\'')
      or newline character may be used to delimit the regular expression.
      Also, putting a backslash character before the delimiting character
      causes the character to be treated literally.  For example, in the
      context address \xabc\xdefx, the RE delimiter is an ``x'' and the
      second ``x'' stands for itself, so that the regular expression is
      ``abcxdef''.

请注意，那里的示例使用了 \xpatternx 而不是 xpatternx.这就是它给出的所有线索，它并没有说明 xpatternx 不起作用.

Notice that the example there uses \xpatternx instead of just xpatternx. That's all the clue it gives, it doesn't make it clear that xpatternx won't work.

基于 @that-other-guy 的论点，sed(以及@Birei 指出的perl 等其他语言)需要这个正确工作的额外线索.

Based on the argument of @that-other-guy, it makes sense that sed (and other languages like perl as @Birei pointed out) need this extra clue to work correctly.

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