How to rewrite the [a-zA-Z0-9!$* \t\r\n] pattern to match hyphen along with the existing characters ?
The hyphen is usually a normal character in regular expressions. Only if it’s in a character class and between two other characters does it take a special meaning.
Thus:
[-] matches a hyphen.
[abc-] matches a, b, c or a hyphen.
[-abc] matches a, b, c or a hyphen.
[ab-d] matches a, b, c or d (only here the hyphen denotes a character range).
Escape the hyphen.
[a-zA-Z0-9!$* \t\r\n\-]
UPDATE:
Never mind this answer - you can add the hyphen to the group but you don't have to escape it. See Konrad Rudolph's answer instead which does a much better job of answering and explains why.
It’s less confusing to always use an escaped hyphen, so that it doesn't have to be positionally dependent. That’s a \- inside the bracketed character class.
But there’s something else to consider. Some of those enumerated characters should possibly be written differently. In some circumstances, they definitely should.
This comparison of regex flavors says that C♯ can use some of the simpler Unicode properties. If you’re dealing with Unicode, you should probably use the general category \p{L} for all possible letters, and maybe \p{Nd} for decimal numbers. Also, if you want to accomodate all that dash punctuation, not just HYPHEN-MINUS, you should use the \p{Pd} property. You might also want to write that sequence of whitespace characters simply as \s, assuming that’s not too general for you.
All together, that works out to apattern of [\p{L}\p{Nd}\p{Pd}!$*] to match any one character from that set.
I’d likely use that anyway, even if I didn’t plan on dealing with the full Unicode set, because it’s a good habit to get into, and because these things often grow beyond their original parameters. Now when you lift it to use in other code, it will still work correctly. If you hard‐code all the characters, it won’t.
[-a-z0-9]+,[a-z0-9-]+,[a-z-0-9]+ and also [a-z-0-9]+ all are same.The hyphen between two ranges considered as a symbol.And also [a-z0-9-+()]+ this regex allow hyphen.
use "\p{Pd}" without quotes to match any type of hyphen. The '-' character is just one type of hyphen which also happens to be a special character in Regex.
Is this what you are after?
MatchCollection matches = Regex.Matches(mystring, "-");
Related
This question seems fairly pedantic, however it feels reasonably important when trying to follow the RFC. I am trying to write an IRC client and I am using the RFC to follow how the protocol should be written. I came across the section for message prefixes and was slightly confused by what was written.
Each IRC message may consist of up to three main parts: the prefix
(optional), the command, and the command parameters (of which there
may be up to 15). The prefix, command, and all parameters are
separated by one (or more) ASCII space character(s) (0x20).
The presence of a prefix is indicated with a single leading ASCII
colon character (':', 0x3b), which must be the first character of the
message itself. There must be no gap (whitespace) between the colon
and the prefix.
My question concerns the first sentence in the second paragraph; ASCII colon character (':', 0x3b). With (to my understanding) 0x3bbeing the ASCII character for a semi-colon, does this mean that the prefix may be either semi-colon or a colon, or is it simply a typo in the document? I'm going ahead with using a colon for now, however my curiosity is nagging away at me.
The colon : (0x3a) is correct.
This is the first errata listed for RFC1459.
What would be the best way to find a word such as Hi or a name mainly like dön with that special char in it through a pattern. They would be optional so it should obviously use a '?' but I dont know what control code to use to find them.
I basically want to make sure that I am getting words with possible unicode characters in them but nothing else. So dön would be fine but no other special chars or numbers and such like brackets.
According to the Lua guide on Unicode, "Lua's pattern matching facilities work byte by byte. In general, this will not work for Unicode pattern matching, although some things will work as you want". This means the best option is probably to iterate over each character and work out if it is a valid letter. To loop over each unicode character in a string:
for character in string.gmatch(myString, "([%z\1-\127\194-\244][\128-\191]*)") do
-- Do something with the character
end
Note this method will not work if myString isn't valid unicode. To check if the character is one that you want, it's probably best to simply have a list of all characters you don't want in your strings and then exclude them:
local notAllowed = ":()[]{}+_-=\|`~,.<>/?!##$%^&*"
local isValid = true
for character in string.gmatch(myString, "([%z\1-\127\194-\244][\128-\191]*)") do
if notAllowed:find(character) then
isValid = false
break
end
end
Hope this helped.
What is the likelihood that I'll run into COMBINING LATIN SMALL LETTER C (U+0368) in "real life" (besides clever Scottish folk)?
I'm asking since it's in both the Unicode Block Combining Diacritical Marks and the Category Mark, Nonspacing [Mn].
As a result, it seems to gets treated the same as characters such as COMBINING GRAVE ACCENT (U+0300) by Utilities such as the ICU Transliterator (using either the suggested "NFD; [:Nonspacing Mark:] Remove; NFC" or a straight "Latin-ASCII" transliteration).
The likelihood is very close to zero, but not exactly zero. You cannot prevent anyone from using a Unicode character as he likes. There is no specific information about U+0368 in the Unicode Standard, but it has definitely been defined as a combining character that will cause a symbol (c) to be displayed above the preceding character. I would expect to find it mostly in digitized forms of medieval manuscripts, or something like that.
Using it after a space character, as in the “clever” page mentioned, is not the intended use, but not invalid either. Unicode lets you use any combining mark after any character, whether it makes sense or not.
It has no canonical or compatibility decomposition, so there is no clear-cut way to deal with in a context where you cannot, or do not want to, retain the character.
The likelihood is utterly indeterminate except to say that if you expect it not to occur, then it will occur.
Does there exist a standard Perl module or function that, given a Unicode Combining Character Sequence (or, more generally, an arbitrary Unicode text string), will generate a list of all canonically equivalent strings?
For example, if given the character U+1EAD, I'd like to get back a list of all these canonically equivalent sequences:
0061 0302 0323
0061 0323 0302
00E2 0323
1EA1 0302
1EAD
(I don't particularly care whether the interface is in terms of arrays of USVs or utf strings.)
Is this an XY problem? If you want to compare/match 2 unicode strings and you're worried that different ways of encoding the accented characters would create false negatives, then the best way to do this would be to normalize the 2 strings using one of the normalization functions from Unicode::Normalize, before doing the comparison or match.
Otherwise it gets a little messy.
You could get the complete character name using charnames::viacode(0x1EAD); (for U+1EAD it would be LATIN SMALL LETTER A WITH CIRCUMFLEX AND DOT BELOW), and get the various composing characters by splitting the name on WITH|AND. Then you could generate all combinations (checking that they exist!) of the base character + modifiers and the other modifiers. At this point you will run into the problem of matching the combining characters names in the full name (eg CIRCUMFLEX) with the combining character real name (COMBINING CIRCUMFLEX ACCENT). There are probably rules for this, but I don't know them.
This would be my naive attempt, there may be better ways of doing this, but since so far no one has volunteered the information...
We are processing IBMEnterprise Japanese COBOL source code.
The rules that describe exactly what is allowed in G type literals,
and what are allowed for identifiers are unclear.
The IBM manual indicates that a G'....' literal
must have a SHIFT-OUT as the first character inside the quotes,
and a SHIFT-IN as the last character before the closing quote.
Our COBOL lexer "knows" this, but objects to G literals
found in real code. Conclusion: the IBM manual is wrong,
or we are misreading it. The customer won't let us see the code,
so it is pretty difficult to diagnose the problem.
EDIT: Revised/extended below text for clarity:
Does anyone know the exact rules of G literal formation,
and how they (don't) match what the IBM reference manuals say?
The ideal answer would a be regular expression for the G literal.
This is what we are using now (coded by another author, sigh):
#token non_numeric_literal_quote_g [STRING]
"<G><squote><ShiftOut> (
(<NotLineOrParagraphSeparatorNorShiftInNorShiftOut>|<squote><squote>|<ShiftOut>)
(<NotLineOrParagraphSeparator>|<squote><squote>)
| <ShiftIn> ( <NotLineOrParagraphSeparatorNorApostropheNorShiftInNorShiftOut>|
<ShiftIn>|<ShiftOut>)
| <squote><squote>
)* <ShiftIn><squote>"
where <name> is a macro that is another regular expression. Presumably they
are named well enough so you can guess what they contain.
Here is the IBM Enterprise COBOL Reference.
Chapter 3 "Character Strings", subheading "DBCS literals" page 32 is relevant reading.
I'm hoping that by providing the exact reference, an experienced IBMer can tell us how we misread it :-{ I'm particularly unclear on what the phrase "DBCS-characters" means
when it says "one or more characters in the range X'00...X'FF for either byte"
How can DBCS-characters be anything but pairs of 8-bit character codes?
The existing RE matches 3 types of pairs of characters if you examine it.
One answer below suggests that the <squote><squote> pairing is wrong.
OK, I might believe that, but that means the RE would only reject
literal strings containing single <squote>s. I don't believe that's
the problem we are having as we seem to trip over every instance of a G literal.
Similarly, COBOL identifiers can apparantly be composed
with DBCS characters. What is allowed for an identifier, exactly?
Again a regular expression would be ideal.
EDIT2: I'm beginning to think the problem might not be the RE.
We are reading Shift-JIS encoded text. Our reader converts that
text to Unicode as it goes. But DBCS characters are really
not Shift-JIS; rather, they are binary-coded data. Likely
what is happening is the that DBCS data is getting translated
as if it were Shift-JIS, and that would muck up the ability
to recognize "two bytes" as a DBCS element. For instance,
if a DBCS character pair were :81 :1F, a ShiftJIS reader
would convert this pair into a single Unicode character,
and its two-byte nature is then lost. If you can't count pairs,
you can't find the end quote. If you can't find the end quote,
you can't recognize the literal. So the problem would appear
to be that we need to switch input-encoding modes in the middle
of the lexing process. Yuk.
Try to add a single quote in your rule to see if it passes by making this change,
<squote><squote> => <squote>{1,2}
If I remember it correctly, one difference between N and G literals is that G allows single quote. Your regular expression doesn't allow that.
EDIT: I thought you got all other DBCS literals working and just having issues with G-string so I just pointed out the difference between N and G. Now I took a closer look at your RE. It has problems. In the Cobol I used, you can mix ASCII with Japanese, for example,
G"ABC<ｦｧｨ>" <> are Shift-out/shift-in
You RE assumes the DBCS only. I would loose this restriction and try again.
I don't think it's possible to handle G literals entirely in regular expression. There is no way to keep track of matching quotes and SO/SI with a finite state machine alone. Your RE is so complicated because it's trying to do the impossible. I would just simplify it and take care of mismatching tokens manually.
You could also face encoding issues. The code could be in EBCDIC (Katakana) or UTF-16, treating it as ASCII will not work. SO/SI sometimes are converted to 0x1E/0x1F on Windows.
I am just trying to help you shoot in the dark without seeing the actual code :)
Does <NotLineOrParagraphSeparatorNorApostropheNorShiftInNorShiftOut> also include single and double quotation marks, or just apostrophes? That would be a problem, as it would consume the literal closing character sequence >' ...
I would check the definition of all other macros to make sure. The only obvious problem that I can see is the <squote><squote> that you already seem to be aware of.