正则表达式以匹配IP地址 [英] Regex to match IP addresses

问题描述

我试图通过正则表达式匹配在 traceroute 输出中找到的IP地址.我不是要验证它们，因为它足以假定 traceroute 是有效的(即不会输出类似 999.999.999.999 的东西.我正在尝试以下正则表达式:

I am trying to match IP addresses found in the output of traceroute by means of a regex. I'm not trying to validate them because it's safe enough to assume traceroute is valid (i.e. is not outputting something like 999.999.999.999. I'm trying the following regex:

([0-9]{1,3}.?){4}

我正在 regex101 中对其进行测试，它确实可以验证IP地址.但是，当我尝试

I'm testing it in regex101 and it does validate an IP address. However, when I try

echo '192.168.1.1 foobar' | grep '([0-9]{1,3}.?){4}' 

我什么也没得到.我想念什么?

I get nothing. What am I missing?

推荐答案

您使用了POSIX ERE模式，但没有通过 -E 选项使 grep 使用POSIX ERE风味.因此， grep 使用POSIX BRE代替，在这里您需要转义 {n，m} 量词和(...)使其成为解析为特殊的正则表达式运算符.

You used a POSIX ERE pattern, but did not pass -E option to have grep use the POSIX ERE flavor. Thus, grep used POSIX BRE instead, where you need to escape {n,m} quantifier and (...) to make them be parsed as special regex operators.

请注意，您需要转义.，以便它只能与文字点匹配.

Note you need to escape a . so that it could only match a literal dot.

要使您的模式与 grep 一起使用，您可以使用以下方式:

To make your pattern work with grep the way you wanted you could use:

grep -E '([0-9]{1,3}\.?){4}'      # POSIX ERE
grep '\([0-9]\{1,3\}\.\?\)\{4\}'  # POSIX BRE version of the same regex

参见在线演示.

但是，由于.是可选的，因此此正则表达式还将匹配多个数字的字符串.

However, this regex will also match a string of several digits because the . is optional.

您可以通过展开模式来解决它

You may solve it by unrolling the pattern as

grep -E '[0-9]{1,3}(\.[0-9]{1,3}){3}'      # POSIX ERE
grep '[0-9]\{1,3\}\(\.[0-9]\{1,3\}\)\{3\}' # POSIX BRE

请参见另一个演示.

基本上，它匹配:

• [0-9] {1,3} -出现1至3次任何ASCII数字
• (\.[0-9] {1,3}){3} -3次出现:
  • \.-文字.
  • [0-9] {1,3} -任意ASCII数字出现1至3次
  • [0-9]{1,3} - 1 to 3 occurrences of any ASCII digit
  • (\.[0-9]{1,3}){3} - 3 occurrences of:
    • \. - a literal .
    • [0-9]{1,3} - 1 to 3 occurrences of any ASCII digit

    为确保仅匹配有效的IP，您可能需要使用更精确的IP匹配正则表达式:

    To make sure you only match valid IPs, you might want to use a more precise IP matching regex:

    grep -E '\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)(\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}\b' # POSIX ERE
    

    请参见此在线演示.

    您可以进一步调整单词边界(可以是 \< / \> 或 \ b )，等等.

    You may further tweak it with word boundaries (can be \< / \> or \b), etc.

    要提取IP ，请对 grep 使用 -o 选项: grep -oE'ERE_pattern'文件/ grep -o'BRE_pattern'文件.

    To extract the IPs use -o option with grep: grep -oE 'ERE_pattern' file / grep -o 'BRE_pattern' file.

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