I'm trying to match a string that can be either empty or have 1 or 2 numbers in it such as the following:
我正在尝试匹配一个字符串，该字符串可以为空或者包含1或2个数字，如下所示：
"" (empty) "1" "23"
“”（空）“1”“23”
String with more numbers or non-numeric characters should not match. My closest guess is the regex:
具有更多数字或非数字字符的字符串不应匹配。我最接近的猜测是正则表达式：
[0-9]{0,2}
[0-9] {0,2}
Which I read to say "the numbers 0 through 9 occurring 0 to 2 times." However, in practice I find that regex also matches longer strings like "333". How is it possible to restrict string length in regular expressions?
我读到的是“数字0到9出现0到2次”。但是，实际上我发现正则表达式也匹配更长的字符串，如“333”。如何在正则表达式中限制字符串长度？
3 个解决方案
#1
40
Use the following regex:
使用以下正则表达式：
^[0-9]{0,2}$
You almost had it -- the ^ and $ characters are anchors that match the beginning and end of the string, respectively.
你几乎拥有它 - ^和$字符分别是匹配字符串开头和结尾的锚点。
For a more in-depth discussion on anchors, see here:
有关锚点的更深入讨论，请参见此处：
[Anchors] do not match any character at all. Instead, they match a position before, after or between characters. They can be used to "anchor" the regex match at a certain position.
[Anchors]根本不匹配任何角色。相反，它们匹配角色之前，之后或之间的位置。它们可用于在正确的位置“锚定”正则表达式匹配。
#2
7
You need to anchor the regex:
你需要锚定正则表达式：
^[0-9]{0,2}$
Otherwise the regex will happily match substrings.
否则正则表达式将很乐意匹配子串。
#3
6
Use the metacharacters for start and end of string:
使用元字符作为字符串的开头和结尾：
^[0-9]{0,2}$
If you don't use them, it matches anywhere in the string, and "12", which matches, is part of "123".
如果你不使用它们，它匹配字符串中的任何地方，匹配的“12”是“123”的一部分。
#1
40
Use the following regex:
使用以下正则表达式：
^[0-9]{0,2}$
You almost had it -- the ^ and $ characters are anchors that match the beginning and end of the string, respectively.
你几乎拥有它 - ^和$字符分别是匹配字符串开头和结尾的锚点。
For a more in-depth discussion on anchors, see here:
有关锚点的更深入讨论，请参见此处：
[Anchors] do not match any character at all. Instead, they match a position before, after or between characters. They can be used to "anchor" the regex match at a certain position.
[Anchors]根本不匹配任何角色。相反，它们匹配角色之前，之后或之间的位置。它们可用于在正确的位置“锚定”正则表达式匹配。
#2
7
You need to anchor the regex:
你需要锚定正则表达式：
^[0-9]{0,2}$
Otherwise the regex will happily match substrings.
否则正则表达式将很乐意匹配子串。
#3
6
Use the metacharacters for start and end of string:
使用元字符作为字符串的开头和结尾：
^[0-9]{0,2}$
If you don't use them, it matches anywhere in the string, and "12", which matches, is part of "123".
如果你不使用它们，它匹配字符串中的任何地方，匹配的“12”是“123”的一部分。