3 ms·
But that isn't even completely true and you miss my point about regex falling outside the domain of "real" regular expresssions. Here's a Perl regex to validate
by dottrap 10y ago
But that isn't even completely true and you miss my point about regex falling outside the domain of "real" regular expresssions. Here's a Perl regex to validate email addresses according to RFC 822 (and it doesn't actually handle everything)
http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html
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Now here's a Lua LPeg example:
https://gist.github.com/daurnimator/3044300 https://gist.github.com/daurnimator/3044300
local P = lpeg.P
local R = lpeg.R
local S = lpeg.S
local V = lpeg.V
local C = lpeg.C
local CHAR = R"\0\127"
local SPACE = S"\40\32"
local CTL = R"\0\31" + P"127"
local specials = S[=[()<>@,;:\".[]]=]
local atom = (CHAR-specials-SPACE-CTL)^1
local dtext = CHAR - S"[]\\\13"
local qtext = CHAR - S'"\\\13'
local quoted_pair = "\\" * CHAR
local domain_literal = P"[" * ( dtext + quoted_pair )^0 + P"]"
local quoted_string = P'"' * ( qtext + quoted_pair )^0 * P'"'
local word = atom + quoted_string
-- Implements an email "addr-spec" according to RFC822
local email = P {
V"addr_spec" ;
addr_spec = V"local_part" * P"@" * C(V"domain") ;
local_part = word * ( P"." * word )^0 ;
domain = V"sub_domain" * ( P"." * V"sub_domain" )^0 ;
sub_domain = V"domain_ref" + domain_literal ;
domain_ref = atom ;
}
If you stay in the realm of "real" (theoretical/CS) regular expressions, then regex doesn't have to be nasty. But the fact is that most people are not doing this and trying to do things way outside of the domain. At this point, all bets are off and other tools may be more correct, more appropriate, and more concise.
Edit: Formatting
- bsder 10y agoAnd you demonstrate my point beautifully. First, "validating" an email address is pointless. This is why I can't use things like "+" or UTF-8 in an email address. You send to the email address and see if you get an error. The only people who should be parsing email addresses are mail programs. And, second, RFC822 actually specifies a grammar so why would you expect a regex to do the job?
- raiph 10y agoPerl 6 Rules reframe parsing along the lines you suggest. https://en.wikipedia.org/wiki/Perl_6_rules https://en.wikipedia.org/wiki/Perl_6_rules contains the grammar used to define Perl's sprintf string formatting notation: grammar Str::SprintfFormat { regex format_token { \%: <index>? <precision>? <modifier>? <directive> } token index { \d+ \$ } token precision { <flags>? <vector>? <precision_count> } token flags { <[\ +0\#\-]>+ } token precision_count { [ <[1-9]>\d* | \* ]? [ \. [ \d* | \* ] ]? } token vector { \*? v } token modifier { ll | <[lhmVqL]> } token directive { <[\%csduoxefgXEGbpniDUOF]> } } You could use these rules like so: if / <Str::SprintfFormat::format_token> / { ... } Perl 6 Rules unify PEGs, regexes, and closures -- "[a] rule used in this way is actually identical to the invocation of a subroutine with the extra semantics and side-effects of pattern matching (e.g., rule invocations can be backtracked)." Have you looked at Perl 6 Rules?
- kbenson 10y agoFirst, referencing that regex is somewhat misleading. That's generally the end result of building the constituent parts through Perl's qr regex object creator, and them combining them into a larger regex[1]. Second, if you want to use a grammea, there's a way to to that in the more complex regex engines, you can use named captures to create a grammar within a regex, and then nun it[2]. 1: http://stackoverflow.com/a/2953742/210749 http://stackoverflow.com/a/2953742/210749 2: http://stackoverflow.com/questions/4840988/the-recognizing-power-of-modern-regexes/4843579#4843579 http://stackoverflow.com/questions/4840988/the-recognizing-p...