regex - Grep 所有不以#(哈希)或贪心空格和#(哈希)开头的行

Question

我正在尝试 grep conf 文件中所有不以

开头的有效行

• 哈希(或)
• 任意数量的空格(0 个或多个)和一个散列

下面的正则表达式似乎不起作用。

grep ^[^[[:blank:]]*#] /opt/logstash/logstash.conf

grep ^[^[[[:blank:]]*#]] /opt/logstash/logstash.conf

grep ^[^[\s]*#] /opt/logstash/logstash.conf

我试图了解我做错了什么。

FWIW，下面的正则表达式有效:

grep -v '^[[:blank:]]*#' /opt/logstash/logstash.conf

Answer 1

首先，如果你不引用你的正则表达式，shell 可能会在 grep 看到它之前展开它，所以你应该总是引用你的 grep 正则表达式。

其次，它们不起作用的原因是:[]，“括号表达式”，匹配它包含的任何元素，或者它们在使用 [^ ...]。您似乎试图匹配否定的字符序列，但这不是 [] 所做的。

此外，在方括号表达式中，字符类不应被双方括号括起来:[^[:blank:]] 而不是 [^[[:blank:]]].

我不确定如果没有 -v 和基本或扩展正则表达式是否可行，但是使用可以执行 Perl 正则表达式的 grep(例如 GNU grep)，您可以使用负面前瞻:

grep -P '^(?![[:blank:]]*#)' /opt/logstash/logstash.conf

这是你的正则表达式失败的原因(假设它们被引用):

• ^[^[[:blank:]]*#] – 匹配任何以零个或多个字符开头的行，而不是文字 [ 或空白，后跟 #]
• ^[^[[[:blank:]]*#]] – 匹配以零个或多个字符开头的任何行，而不是文字 [ 或空白(括号表达式中重复的 [[ 与单个 [ 相同)，后跟 #]]
• ^[^[\s]*#] – 匹配以 [, \ 以外的零个或多个字符开头的任何行或 s(\s 在 [] 中并不特殊)，后跟 #]。

如果我们拿这个测试文件:

# comment
normal line
    normal line after spaces
    # comment after spaces
    normal line after tab
    # comment after tab
abc#] does not start with blank or [ and has #]
[abc#] starts with [ and has #]
abc#]] does not start with blank or [ and has #]]
 abc#]] starts with blank and has #]]
sabc#]] starts with s and has #]]
\abc#]] starts with \ and has #]]

表达式匹配如下:

• 您的 grep -v(有效):

  $ grep -v '^[[:blank:]]*#' infile
  normal line
      normal line after spaces
      normal line after tab
  abc#] does not start with blank or [ and has #]
  [abc#] starts with [ and has #]
  abc#]] does not start with blank or [ and has #]]
   abc#]] starts with blank and has #]]
  sabc#]] starts with s and has #]]
  \abc#]] starts with \ and has #]]
  

• 我的 grep -P(有效):

  $ grep -P '^(?![[:blank:]]*#)' infile
  normal line
      normal line after spaces
      normal line after tab
  abc#] does not start with blank or [ and has #]
  [abc#] starts with [ and has #]
  abc#]] does not start with blank or [ and has #]]
   abc#]] starts with blank and has #]]
  sabc#]] starts with s and has #]]
  \abc#]] starts with \ and has #]]
  

• 您的第一次尝试:

  $ grep '^[^[[:blank:]]*#]' infile
  abc#] does not start with blank or [ and has #]
  abc#]] does not start with blank or [ and has #]]
  sabc#]] starts with s and has #]]
  \abc#]] starts with \ and has #]]
  

• 你的第二次尝试:

  $ grep '^[^[[[:blank:]]*#]]' infile
  abc#]] does not start with blank or [ and has #]]
  sabc#]] starts with s and has #]]
  \abc#]] starts with \ and has #]]
  

• 第三次尝试:

  $ grep '^[^[\s]*#]' infile
  abc#] does not start with blank or [ and has #]
  abc#]] does not start with blank or [ and has #]]
   abc#]] starts with blank and has #]]