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Regex Isn't Hard (2023)

(timkellogg.me)
75 points asicsp | 2 comments | 21 Apr 25 10:35 UTC | HN request time: 1.988s | source
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michaelt ◴[21 Apr 25 11:01 UTC] No.43750496[source]▶
> e.g. This pattern ([0-9][0-9]?[0-9]][.])+ matches one, two or three digits followed by a . and also matches repeated patterns of this. This wold match an IP address (albeit not strictly).

I love regular expressions but one thing I've learned over the years is the syntax is dense enough that even people who are confident enough to start writing regex tutorials often can't write a regex that matches an IP address.

replies(9): >>43750531 #>>43750628 #>>43750641 #>>43750693 #>>43750726 #>>43751250 #>>43751329 #>>43751632 #>>43754055 #
reverendsteveii ◴[21 Apr 25 17:01 UTC] No.43754055[source]▶
I haven't verified it but quick googling for a regex to validate all legal email addresses pointed me to https://stackoverflow.com/questions/201323/how-can-i-validat..., where one commenter posits that regex to be:

(?:(?:\r\n)?[ \t])(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?: \r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:( ?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\0 31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\ ](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+ (?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?: (?:\r\n)?[ \t])))|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n) ?[ \t]))\<(?:(?:\r\n)?[ \t])(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\ r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n) ?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t] )))(?:,@(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])* )(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))) :(?:(?:\r\n)?[ \t]))?(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+ |\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r \n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?: \r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t ]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031 ]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\]( ?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(? :(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(? :\r\n)?[ \t])))\>(?:(?:\r\n)?[ \t]))|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(? :(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)? [ \t]))"(?:(?:\r\n)?[ \t])):(?:(?:\r\n)?[ \t])(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]| \\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>

@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|" (?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t] )(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(? :[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[ \]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))|(?:[^()<>@,;:\\".\[\] \000- \031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|( ?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))\<(?:(?:\r\n)?[ \t])(?:@(?:[^()<>@,; :\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([ ^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\" .\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\ ]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))(?:,@(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\ [\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\ r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\] |\\.)\](?:(?:\r\n)?[ \t])))):(?:(?:\r\n)?[ \t]))?(?:[^()<>@,;:\\".\[\] \0 00-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\ .|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[^()<>@, ;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(? :[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t])* (?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\". \[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t])(?:[ ^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\] ]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))\>(?:(?:\r\n)?[ \t]))(?:,\s( ?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))(?:\.(?:( ?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[ \["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t ])))@(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t ])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(? :\.(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+| \Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))|(?: [^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\ ]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))\<(?:(?:\r\n) ?[ \t])(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[" ()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n) ?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>

@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))(?:,@(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@, ;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\.(?:(?:\r\n)?[ \t] )(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))):(?:(?:\r\n)?[ \t]))? (?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\". \[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))(?:\.(?:(?: \r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[ "()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]) ))@(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t]) +|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t]))(?:\ .(?:(?:\r\n)?[ \t])(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)\](?:(?:\r\n)?[ \t])))\>(?:( ?:\r\n)?[ \t]))))?;\s)

Someone else then asks the absolute razor of a question: 'What value does this add over just verifying that the input is of the form {something}@{something}.{something}?'

replies(1): >>43755438 #
1. Supermancho ◴[21 Apr 25 19:17 UTC] No.43755438[source]▶
> 'What value does this add over just verifying that the input is of the form {something}@{something}.{something}?'

Depends if {something} can contain periods for my email.

name@antispam.mydomain.com

replies(1): >>43762827 #
2. reverendsteveii ◴[22 Apr 25 14:44 UTC] No.43762827[source]▶
something is defined as any string of valid characters greater than 0 in length. I'm sure there's some char somewhere that breaks this but in a realistic setting with normal users you won't encounter that edge case and if you do the worst that happens is an email gets returned as non-deliverable