OS X sed -E 不接受扩展的正则表达式
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【中文标题】OS X sed -E 不接受扩展的正则表达式【英文标题】：OS X sed -E doesn't accept extended regular expressions 【发布时间】：2012-08-24 02:55:20 【问题描述】：我一直在尝试各种方法来在 OS X 上使用 sed 做一些基本的事情。以下是一些简单测试的结果。
echo "foo bar 2011-03-17 17:31:47 foo bar" | sed 's/foo/FOUND/g'
返回（如预期）
FOUND bar 2011-03-17 17:31:47 FOUND bar
但是
echo "foo bar 2011-03-17 17:31:47 foo bar" | sed -E 's/\d4-\d2-\d2 \d2:\d2:\d2/FOUND/g'
返回
foo bar 2011-03-17 17:31:47 foo bar
而且（更令人恼火）
echo "food bar 2011-03-17 17:31:47 food bar" | sed -E 's/\d/FOUND/g'
返回
fooFOUND bar 2011-03-17 17:31:47 fooFOUND bar
现在，man sed 页面这么说
The following options are available:
-E Interpret regular expressions as extended (modern) regular
expressions rather than basic regular expressions (BRE's). The
re_format(7) manual page fully describes both formats.
和man re_format 说
\d Matches a digit character. This is equivalent to
`[[:digit:]]'.
确实：
echo "foo bar 2011-03-17 17:31:47 foo bar" | sed -E 's/[[:digit:]]4/FOUND/g'
给我
foo bar FOUND-03-17 17:31:47 foo bar
...但这很烦人。要么是因为我很密集，要么是因为手册页对我撒谎（老实说，我更喜欢前者）。
关于 SO 的快速文献回顾表明，我并不孤单，许多人建议安装 GNU coreutils（或者确实使用其他东西 - 比如说 perl -pe）——但是，我想确定：
ERE 是否可以与sed 一起使用，因为它与 OS X 捆绑在一起——正如 man 页面所暗示的那样——或者不？
（我在 10.8 和 10.6.8）
【问题讨论】：
【参考方案1】：在 macOS 上，\d 是称为 enhanced features 的正则表达式功能集的一部分 - 请注意名称上的区别： 增强，与扩展不同。
相反，增强功能是独立于基本与扩展的维度>，可以为基本和扩展正则表达式激活。换句话说：您可以拥有增强的基本正则表达式以及增强的扩展正则表达式。
但是，给定实用程序中是否提供增强功能似乎已预编译到其中；换句话说：给定的实用程序要么支持增强 功能，要么不支持 - 没有选项可以改变它。
（选项只允许您在 basic 和 extended 之间进行选择，例如 -E 代表 sed 和 grep。）
有关所有增强功能的描述，请参阅man re_format 中的ENHANCED FEATURES 部分。
还应注意，如果 POSIX 兼容性很重要，则应避免使用 sed 增强功能。
有 POSIX 实用程序，例如awk，确实 支持 ERE（扩展正则表达式），但是 (a)，POSIX 规范明确必须这样说明，并且 (b) 语法仅限于 POSIX EREs，其功能不如特定平台提供的 ERE。
在实践中：
遗憾的是，各种实用程序的 man 页面并未说明给定实用程序是否支持增强正则表达式功能，因此它归结为反复试验。
从 macOS 10.15 开始：
macOS sed 不支持增强功能，这说明了 OP 的体验。
sed -E 's/\d//g' <<<'a10' 无效，因为 \d 不被识别为代表数字（只有 [[:digit:]] 是）。
我发现只有一个实用程序支持增强功能：grep：
grep -o '\d\+' <<<'a10' # -> '10' - enhanced basic regex
grep -E -o '\d+' <<<'a10' # -> '10' - enhanced extended regex
如果您知道其他人这样做，请告诉我们。
【讨论】：
令人沮丧的消息，但感谢您的彻底挖掘，@mklement0。 这很令人沮丧.. 编写可移植 sed 脚本的最佳实践是什么？ @Student：您将不得不使用仅限 POSIX 的功能，特别是仅使用 POSIX EREs，并遵守here 概述的其他约束。【参考方案2】：ERE（扩展正则表达式）在 POSIX 中的（惊喜）Regular Expressions 下或在 Mac OS X 上的man re_format 下进行了描述。 ERE 不使用 PCRE 样式 \d 表示法来表示数字。
您需要使用[0-9] 或[[:digit:]] 来表示数字。
$ echo "foo bar 2011-03-17 17:31:47 foo bar" |
> sed -E 's/[0-9]4-[0-9]2-[0-9]2 [0-9]2:[0-9]2:[0-9]2/FOUND/g'
foo bar FOUND foo bar
$ echo "foo bar 2011-03-17 17:31:47 foo bar" |
> sed -E 's/[[:digit:]]4-[[:digit:]]2-[[:digit:]]2 [[:digit:]]2:[[:digit:]]2:[[:digit:]]2/FOUND/g'
foo bar FOUND foo bar
$
\d 呢？
在我的 Mac OS X (10.7.4) 上，man re_format 没有说明 \d 匹配的数字。
RE_FORMAT(7) BSD Miscellaneous Information Manual RE_FORMAT(7)
NAME
re_format -- POSIX 1003.2 regular expressions
DESCRIPTION
Regular expressions (``REs''), as defined in IEEE Std 1003.2
(``POSIX.2''), come in two forms: modern REs (roughly those of egrep(1);
1003.2 calls these ``extended'' REs) and obsolete REs (roughly those of
ed(1); 1003.2 ``basic'' REs). Obsolete REs mostly exist for backward
compatibility in some old programs; they will be discussed at the end.
IEEE Std 1003.2 (``POSIX.2'') leaves some aspects of RE syntax and seman-
tics open; `=' marks decisions on these aspects that may not be fully
portable to other IEEE Std 1003.2 (``POSIX.2'') implementations.
A (modern) RE is one= or more non-empty= branches, separated by `|'. It
matches anything that matches one of the branches.
A branch is one= or more pieces, concatenated. It matches a match for
the first, followed by a match for the second, etc.
A piece is an atom possibly followed by a single= `*', `+', `?', or
bound. An atom followed by `*' matches a sequence of 0 or more matches
of the atom. An atom followed by `+' matches a sequence of 1 or more
matches of the atom. An atom followed by `?' matches a sequence of 0 or
1 matches of the atom.
A bound is `' followed by an unsigned decimal integer, possibly followed
by `,' possibly followed by another unsigned decimal integer, always fol-
lowed by `'. The integers must lie between 0 and RE_DUP_MAX (255=)
inclusive, and if there are two of them, the first may not exceed the
second. An atom followed by a bound containing one integer i and no
comma matches a sequence of exactly i matches of the atom. An atom fol-
lowed by a bound containing one integer i and a comma matches a sequence
of i or more matches of the atom. An atom followed by a bound containing
two integers i and j matches a sequence of i through j (inclusive)
matches of the atom.
An atom is a regular expression enclosed in `()' (matching a match for
the regular expression), an empty set of `()' (matching the null
string)=, a bracket expression (see below), `.' (matching any single
character), `^' (matching the null string at the beginning of a line),
`$' (matching the null string at the end of a line), a `\' followed by
one of the characters `^.[$()|*+?\' (matching that character taken as an
ordinary character), a `\' followed by any other character= (matching
that character taken as an ordinary character, as if the `\' had not been
present=), or a single character with no other significance (matching
that character). A `' followed by a character other than a digit is an
ordinary character, not the beginning of a bound=. It is illegal to end
an RE with `\'.
A bracket expression is a list of characters enclosed in `[]'. It nor-
mally matches any single character from the list (but see below). If the
list begins with `^', it matches any single character (but see below) not
from the rest of the list. If two characters in the list are separated
by `-', this is shorthand for the full range of characters between those
two (inclusive) in the collating sequence, e.g. `[0-9]' in ASCII matches
any decimal digit. It is illegal= for two ranges to share an endpoint,
e.g. `a-c-e'. Ranges are very collating-sequence-dependent, and portable
programs should avoid relying on them.
To include a literal `]' in the list, make it the first character (fol-
lowing a possible `^'). To include a literal `-', make it the first or
last character, or the second endpoint of a range. To use a literal `-'
as the first endpoint of a range, enclose it in `[.' and `.]' to make it
a collating element (see below). With the exception of these and some
combinations using `[' (see next paragraphs), all other special charac-
ters, including `\', lose their special significance within a bracket
expression.
Within a bracket expression, a collating element (a character, a multi-
character sequence that collates as if it were a single character, or a
collating-sequence name for either) enclosed in `[.' and `.]' stands for
the sequence of characters of that collating element. The sequence is a
single element of the bracket expression's list. A bracket expression
containing a multi-character collating element can thus match more than
one character, e.g. if the collating sequence includes a `ch' collating
element, then the RE `[[.ch.]]*c' matches the first five characters of
`chchcc'.
Within a bracket expression, a collating element enclosed in `[=' and
`=]' is an equivalence class, standing for the sequences of characters of
all collating elements equivalent to that one, including itself. (If
there are no other equivalent collating elements, the treatment is as if
the enclosing delimiters were `[.' and `.]'.) For example, if `x' and
`y' are the members of an equivalence class, then `[[=x=]]', `[[=y=]]',
and `[xy]' are all synonymous. An equivalence class may not= be an end-
point of a range.
Within a bracket expression, the name of a character class enclosed in
`[:' and `:]' stands for the list of all characters belonging to that
class. Standard character class names are:
alnum digit punct
alpha graph space
blank lower upper
cntrl print xdigit
These stand for the character classes defined in ctype(3). A locale may
provide others. A character class may not be used as an endpoint of a
range.
A bracketed expression like `[[:class:]]' can be used to match a single
character that belongs to a character class. The reverse, matching any
character that does not belong to a specific class, the negation operator
of bracket expressions may be used: `[^[:class:]]'.
There are two special cases= of bracket expressions: the bracket expres-
sions `[[:<:]]' and `[[:>:]]' match the null string at the beginning and
end of a word respectively. A word is defined as a sequence of word
characters which is neither preceded nor followed by word characters. A
word character is an alnum character (as defined by ctype(3)) or an
underscore. This is an extension, compatible with but not specified by
IEEE Std 1003.2 (``POSIX.2''), and should be used with caution in soft-
ware intended to be portable to other systems.
In the event that an RE could match more than one substring of a given
string, the RE matches the one starting earliest in the string. If the
RE could match more than one substring starting at that point, it matches
the longest. Subexpressions also match the longest possible substrings,
subject to the constraint that the whole match be as long as possible,
with subexpressions starting earlier in the RE taking priority over ones
starting later. Note that higher-level subexpressions thus take priority
over their lower-level component subexpressions.
Match lengths are measured in characters, not collating elements. A null
string is considered longer than no match at all. For example, `bb*'
matches the three middle characters of `abbbc',
`(wee|week)(knights|nights)' matches all ten characters of `weeknights',
when `(.*).*' is matched against `abc' the parenthesized subexpression
matches all three characters, and when `(a*)*' is matched against `bc'
both the whole RE and the parenthesized subexpression match the null
string.
If case-independent matching is specified, the effect is much as if all
case distinctions had vanished from the alphabet. When an alphabetic
that exists in multiple cases appears as an ordinary character outside a
bracket expression, it is effectively transformed into a bracket expres-
sion containing both cases, e.g. `x' becomes `[xX]'. When it appears
inside a bracket expression, all case counterparts of it are added to the
bracket expression, so that (e.g.) `[x]' becomes `[xX]' and `[^x]'
becomes `[^xX]'.
No particular limit is imposed on the length of REs=. Programs intended
to be portable should not employ REs longer than 256 bytes, as an imple-
mentation can refuse to accept such REs and remain POSIX-compliant.
Obsolete (``basic'') regular expressions differ in several respects. `|'
is an ordinary character and there is no equivalent for its functional-
ity. `+' and `?' are ordinary characters, and their functionality can be
expressed using bounds (`1,' or `0,1' respectively). Also note that
`x+' in modern REs is equivalent to `xx*'. The delimiters for bounds are
`\' and `\', with `' and `' by themselves ordinary characters. The
parentheses for nested subexpressions are `\(' and `\)', with `(' and `)'
by themselves ordinary characters. `^' is an ordinary character except
at the beginning of the RE or= the beginning of a parenthesized subex-
pression, `$' is an ordinary character except at the end of the RE or=
the end of a parenthesized subexpression, and `*' is an ordinary charac-
ter if it appears at the beginning of the RE or the beginning of a paren-
thesized subexpression (after a possible leading `^'). Finally, there is
one new type of atom, a back reference: `\' followed by a non-zero deci-
mal digit d matches the same sequence of characters matched by the dth
parenthesized subexpression (numbering subexpressions by the positions of
their opening parentheses, left to right), so that (e.g.) `\([bc]\)\1'
matches `bb' or `cc' but not `bc'.
SEE ALSO
regex(3)
Regular Expression Notation, IEEE Std, 1003.2, section 2.8.
BUGS
Having two kinds of REs is a botch.
The current IEEE Std 1003.2 (``POSIX.2'') spec says that `)' is an ordi-
nary character in the absence of an unmatched `('; this was an uninten-
tional result of a wording error, and change is likely. Avoid relying on
it.
Back references are a dreadful botch, posing major problems for efficient
implementations. They are also somewhat vaguely defined (does
`a\(\(b\)*\2\)*d' match `abbbd'?). Avoid using them.
IEEE Std 1003.2 (``POSIX.2'') specification of case-independent matching
is vague. The ``one case implies all cases'' definition given above is
current consensus among implementors as to the right interpretation.
The syntax for word boundaries is incredibly ugly.
BSD March 20, 1994 BSD
【讨论】：
多么非常奇怪。我的man re_format 在 10.8 上显示的发布日期为“2011 年 9 月 29 日”，但我的 10.6.8 机器的页面与您的相同。碰巧的是，/d 只是我的问题的陪衬。我实际上对\w 和\W 更感兴趣，它们没有（整洁的）替代品。但我想，你帮我找出了问题所在。另外——非常感谢您指出 PCRE 不是 ERE。这将阻止我在未来变得更加愚蠢。
在 10.8.3 中，2011 年 9 月 29 日发布的 re_format 页面在“增强功能”下提到了所有各种转义字符类（\d、\w、\s 等）。但是，使用 sed -E 它们似乎根本不起作用。事实上， sed -E 's/\s//' 匹配每行的第一个 's'，而不是预期的空白。发现这个 SO question 试图找出原因。
10.8.3 man sed 说：-E 将正则表达式解释为扩展（现代）正则表达式，而不是基本正则表达式（BRE）。 re_format(7) 手册页全面描述了这两种格式。 这不包括激活man re_format 中描述的\d 和\s 符号所必需的“增强”一词。 -E 选项确实意味着 sed -E 's/(ke|st)/xx/g' 在输入上全局替换 ke 或 st 为 xx。所以，-E 表示扩展，但不是增强扩展。
呃。我想我只是要编写自己的节点脚本来进行就地正则表达式替换。
这并不完全准确。正如@mklement0 在第二个答案中指出的那样，“扩展”和“增强”功能是不同的。请注意man 7 re_format 上描述和增强功能的第一段。 IEEE 1003.2 (POSIX.2) 定义了过时/基本和现代/扩展的正则表达式。 enhanced 特性是可能与标准冲突的附加规则（略超过 re_format 文档的一半）。 OS X egrep 支持增强的 功能，但不支持 sed。以上是关于OS X sed -E 不接受扩展的正则表达式的主要内容，如果未能解决你的问题，请参考以下文章