May I know what ?= means in a regular expression? For example, what is its significance in this expression:
我可以知道什么意思吗?例如，这个表达的意义是什么?
(?=.*\d).
3 个解决方案
#1
36
?= is a positive lookahead, a type of zero-width assertion. What it's saying is that the captured match must be followed by whatever is within the parentheses but that part isn't captured.
是一个正向的展望，一种零宽度的断言。它的意思是捕获的匹配必须后面跟着括号内的任何东西，但是那个部分没有被捕获。
Your example means the match needs to be followed by zero or more characters and then a digit (but again that part isn't captured).
您的示例意味着匹配之后需要0个或多个字符，然后是一个数字(但同样地，这个部分没有被捕获)。
#2
0
The below expression will find the last number set in a filename before its extension (excluding dot (.)).
下面的表达式将找到扩展之前文件名中的最后一个数字集(不包括点(.))。
'\d+(?=\.\w+$)'
file4.txt will match 4.
file4。三种匹配4。
file123.txt will match 123.
file123。txt将匹配123。
demo.3.js will match 3 and so on.
demo.3。js将匹配3，以此类推。
#3
-1
(?=pattern) is a zero-width positive lookahead assertion. For example, /\w+(?=\t)/ matches a word followed by a tab, without including the tab in $&.
(?=pattern)是一个零宽度的正向前视断言。例如，/\w+(?=\t)/匹配一个单词后跟一个标签，而不包含$&中的标签。
#1
36
?= is a positive lookahead, a type of zero-width assertion. What it's saying is that the captured match must be followed by whatever is within the parentheses but that part isn't captured.
是一个正向的展望，一种零宽度的断言。它的意思是捕获的匹配必须后面跟着括号内的任何东西，但是那个部分没有被捕获。
Your example means the match needs to be followed by zero or more characters and then a digit (but again that part isn't captured).
您的示例意味着匹配之后需要0个或多个字符，然后是一个数字(但同样地，这个部分没有被捕获)。
#2
0
The below expression will find the last number set in a filename before its extension (excluding dot (.)).
下面的表达式将找到扩展之前文件名中的最后一个数字集(不包括点(.))。
'\d+(?=\.\w+$)'
file4.txt will match 4.
file4。三种匹配4。
file123.txt will match 123.
file123。txt将匹配123。
demo.3.js will match 3 and so on.
demo.3。js将匹配3，以此类推。
#3
-1
(?=pattern) is a zero-width positive lookahead assertion. For example, /\w+(?=\t)/ matches a word followed by a tab, without including the tab in $&.
(?=pattern)是一个零宽度的正向前视断言。例如，/\w+(?=\t)/匹配一个单词后跟一个标签，而不包含$&中的标签。