如何使用正则表达式匹配此模式

Question

我是 ruby​​ 的新手并尝试使用正则表达式。 基本上我想读取一个文件并检查它是否具有正确的格式。

Requirements to be in the correct format:
1: The word should start with from
2: There should be one space and only one space is allowed, unless there is a comma 
3: Not consecutive commas
4: from and to are numbers
5: from and to must contain a colon

from: z to: 2
from: 1 to: 3,4
from: 2 to: 3
from:3 to: 5 
from: 4 to: 5
from: 4 to: 7
to: 7 from: 6 
from: 7 to: 5
0: 7 to: 5
from: 24 to: 5
from: 7 to: ,,,5
from: 8 to: 5,,5
from: 9 to: ,5

如果我有正确的正则表达式，那么输出应该是：

from: 1 to: 3,4
from: 2 to: 3
from: 4 to: 5
from: 4 to: 7
from: 7 to: 5
from: 24 to: 5

所以在这种情况下，这些是错误的：

from: z to: 2     # because starts with z
from:3 to: 5      # because there is no space after from:
to: 7 from: 6     # because it starts with to but supposed to start with from
0: 7 to: 5        # starts with 0 instead of from
from: 7 to: ,,,5  # because there are two consecutive commas
from: 8 to: 5,,5  # two consecutive commas
from: 9 to: ,5    # start with comma

Answer 1

好的，你想要的正则表达式是这样的：

from: \d+(?:,\d+)* to: \d+(?:,\d+)*

这假设在from:列中也允许多个数字。 如果没有，你想要这个：

from: \d+ to: \d+(?:,\d+)*

要验证整个文件是否有效（假设它包含的所有行都是这样的），您可以使用这样的函数：

def validFile(filename)
    File.open(filename).each do |line|
        return false if (!/\d+(?:,\d+)* to: \d+(?:,\d+)*/.match(line))
    end
    return true
end

Answer 2

您正在寻找的称为负前瞻。 具体来说， \\d+(?!,,)表示：匹配 1 个或多个连续数字，后面不跟 2 个逗号。 这是整个事情：

str = "from: z to: 2
from: 1 to: 3,4
from: 2 to: 3
from:3 to: 5 
from: 4 to: 5
from: 4 to: 7
to: 7 from: 6 
from: 7 to: 5
0: 7 to: 5
from: 24 to: 5
from: 7 to: ,,,5
from: 8 to: 5,,5
from: 9 to: ,5
"

str.each_line do |line|
  puts(line) if line =~ /\Afrom: \d+ to: \d+(?!,,)/
end

输出：

from: 1 to: 3,4
from: 2 to: 3
from: 4 to: 5
from: 4 to: 7
from: 7 to: 5
from: 24 to: 5