Regex Multiline

[SmallSmartMouse]

a regex= ^(ac|bb)$\n, but this i dont use option Multiline,I think it will error when MustCompile,but it not ,and can match string "ac\n",so how can i do ,it will throw an error

[dlclark]

Hello!
I believe this is a difference in behavior between PCRE and Javascript/RE2 regex engines. You can see this by changing the engine on the left side here: https://regex101.com/r/hUAttU/1
Go (RE2) and Javascript don't match, but PHP/PCRE and Python do.

The definition for $ in PCRE-based engines without Multiline is: $ asserts position at the end of the string, or before the line terminator right at the end of the string (if any). That means that the pattern $\n will match the text \n -- the $ will match the newline but is zero-width so it won't advance the pattern, and then the explicit \n will match and advance the pattern.

Honestly the behavior is counter-intuitive, but it's an edge case that I maintain for compatibility with the other Javascript engines (including C#, Python, and PCRE). I recently added an RE option to increase compatibility with existing Go regex's when needed -- would you like me to add this case to it?

If I misunderstood please provide a code example so I can review it in more detail.

Thanks!

[dop251]

Sorry, just spotted this. I'd like that fixed at least for ECMAScript mode if possible. Thanks!

[dlclark]

I’ll have to put this change behind the RE2 or EMCAScript options.

I might have some time to do it this week.

[dop251]

Thanks!