How do i remove   — – special characters from my XML files - ruby

this is a sample of the xml file
<row tnote="0">
<entry namest="col2" nameend="col4" us="none" emph="bld"><blst>
<li><text>Single, head of household, or qualifying widow(er)—$55,000</text></li>
<li><text>Married filing jointly—$115,000</text></li>
</blst></entry>
<entry colname="col6" ldr="1" valign="middle"> </entry>
<entry colname="col7" valign="middle"> 5.</entry>
</row>
the — etc represent HTML 4.0 entities. i want to store each line's text as an element of an array, but not if the line is just  
if e.text.strip =~ /^&#x20[0-9][0-9];$/ then
next
else
subLines << e.text
end
but it doesn't seem to be working...is my regEx incorrect?

&#x...; isn't an entity reference, it's a character reference. To an XML parser, — is absolutely identical to the raw character —, so when you look at the DOM produced by an XML parser through a property such as element.text you won't see anything with an ampersand in it, but a simple — character.
So in principle, you'd match it with a regex something like /[—– ]/. However, if you are using Ruby 1.8, you've got the problem that the language itself doesn't have support for Unicode, so the character group in /[—– ]/ won't quite work properly: it'll try to remove every byte in the UTF-8 representation of –, — and  , which will likely mangle any other characters.
A simple string replace for each target character would work correctly, as that doesn't require special character handling. (Naturally if you included characters like — directly in the source code you'd also have to get the file encoding of that script right, so probably easier to use a string literal escape like "\xe2\x80\x94".)

Because your regex is of the form /^...$/, it will only match against the entire string. You will only skip text that consists entirely of one HTML entity.

Related

Can I treat all domain names as being IDNs without any ill effects?

From testing, it seems like trying to convert both IDNs and regular domain names 'just works' - eg, if the input doesn't need to be changed punycode will just return the input.
punycode.toASCII('lancôme.com');
returns:
'xn--lancme-lxa.com'
And
punycode.toASCII('apple.com');
returns:
'apple.com'
This looks great, but is it specified anywhere? Can I safely convert everything to punycode?
That is correct. If you look at how the procedure for converting unicode strings to ascii punycode, the process only alters any non-ascii character. Since regular domains cannot contain non-ascii characters, if your conversor is correctly implemented, it will never transform any pure-ascii string.
You can read more about how unicode is converted to punycode here: https://en.wikipedia.org/wiki/Punycode
Punycode is specified in RFC 3492: https://www.ietf.org/rfc/rfc3492.txt, and it clearly says:
"Basic code point segregation" is a very simple and
efficient encoding for basic code points occurring in the extended
string: they are simply copied all at once.
Therefore, if your extended string is made of basic code points, it will just be copied without change.

What characters are never used in xpath?

I'm trying to build a DSL which will contain a number of XPaths as parameters. I'm new to XPath, and I need a character which is never used in the XPath syntax so I can delimit n number of XPaths on a single line of a script. My question: what characters are NOT part of the XPath syntax?
The null character.
Seriously. Because an XPath is supposed to support any XML document, it must be capable of matching text nodes that contain any allowed Unicode character. However, XML disallows one character: the null character.
Ok, that is not entirely true, but it is simplest. As in XML 1.1, control characters were supported, except Unicode Null. However, as per the XML 1.0 production of Char, there are a few other characters you can choose from: surrogate pairs (as characters, not as correctly encoded octets representing a non-BMP character), and anything before 0x20, except linefeed, carriage return and tab.
Another good guess is any Private Use character, as it is unlikely it is used by your input documents, however, this is not guaranteed, and you asked for "never".
I'm trying to build a DSL which will contain a number of XPaths as parameters.
Well, many people use XML for DSLs, and this is how you would do it in XML:
<paths>
<path>/a/b/c/d</path>
<path>/w/x/y/z</path>
</path>
So how do we reconcile this with the fact that "<" can appear in an XPath expression? Answer: if it does appear, we escape it:
<paths>
<path>/a/b/c/d[e < 3]</path>
<path>/w/x/y/z[v < 2]</path>
</path>
So: don't try to find a character that can't appear in an XPath expression. Use a character that can appear, and escape it if it does.

ISO-8859-1 characters treated as UTF-8 in XSLT attributes

The ¬ character (0xAC in ISO-8859-1) works for normal text if I ensure that ISO-8859-1 is always used as the encoding throughout. However, when using it in attributes it is escaped to: %C2%AC. I understand that it needs to be escaped for urls, but not why it escapes it in the same way as it would for UTF-8, rather than just %AC as I'd expect it to for ISO-8859-1.
Since the escapes are in the output html file the only conclusion is that the xslt processor is the cause.
Example:
input.xml
stylesheet.xslt
makefile
Which for me generates:
output.html
Output was generated using xsltproc, compiled against libxml 20707, libxslt 10126 and libexslt 815. This was on #! Linux (amd64). I have also tried: xmlstarlet tr (also uses libxml), xalan and google chrome (by adding an <?xml-stylesheet ... >, see input_ss.xml tag) with the same result.
Opera doesn't escape it at all, and it allows ¬ to be used literally in the url and attribute.
Is this standard behaviour for xslt or is this a bug in the way the attributes are escaped? And either way, is there a solution other than replacing %C2%AC with %AC bearing in mind it is almost certainly the same for other characters that are valid ISO-8859-1 and invalid in UTF-8.
There are 3 different text-based technologies in use here, XML, HTML and URIs.
All of these have escape mechanisms - that is to say, ways to use text to indicate other text that it is impossible or difficult to indicate in a given context.
The not-sign character ¬ (U+00AC) could be escaped in the first two as ¬ or ¬ perhaps with some leading zeros, in both XML and HTML (¬ would also work in HTML). This escape would be used no matter what encoding the XML or HTML was in, because it relates to the character ¬, not to its set of octets in a given character encoding - indeed, we would generally only use it in the case where there was no such set of octets in the encoding being used.
In this case, this is unnecessary, since the output is in a character encoding in which there is no need to escape it, and so in the source you can see The ¬ character unescaped.
This HTML includes the text of a URI. The encoding of the HTML has nothing to do with this, because the encoding is how we get the text of the HTML from one machine to another, but when the HTML is being parsed to read this URI we're past that point and are dealing with some text at the level of text - that is to say, it doesn't have an encoding any more.
Now, URIs have their own escape mechanisms. This must be used in the case of ¬, as it is not a character allowed in URIs (as opposed to IRIs). Sadly, unlike the escapes in XML and HTML, these escapes are based on octets in a given encoding rather than the code-point of the character itself.
It's easy to see this as a mistake now, but URIs were specified in 1994 and that formalised work going back to 1989/1990 while Unicode 1.0 was released in 1991 and didn't have the ground-breaking 2.0 until 1996, so hindsight has considerably more benefits than URI's inventors. (HTML had the same problem many years ago, but the format of its encodings made it much easier to fix this without as many backwards-compatibility issues).
So, what encoding should we use for those octets? The original specs left this undefined, but really the only possible choice is UTF-8. It's the only encoding that gives those escapes commonly used for chracters special to URIs their escapes in the range 0x20 - 0x7F while also covering all of the UCS.
There's also no way to indicate another choice could be more appropriate. Remember, we're working at the level of text, so your use of ISO-8859-1 is completely irrelevant. Even if we kept track of the encoding while parsing the HTML, the URI is going to be made use of in a way that is nothing to do with the document, so we still couldn't use it. In all, if we have to make use of an octet-based encoding, and we have to keep characters in the ASCII range matching the octets they'd have in ASCII, the only possible basis for the encoding is UTF-8.
For that reason, the escape in any URI for ¬ must always be %C2%AC.
There can be some legacy systems that expect URIs to use other encodings, but the solution is to fix the bit that's broken, not the bit that works, so if something expects ¬ to be %AC then catch it close to that by converting %C2%AC close to its use (and if it outputs %AC itself then of course you'll need to fix it to %C2%AC before it hits the outside world).
The XSLT spec says that when serializing URI-valued attributes, all non-ASCII characters are escaped using the %HH-escaping of the UTF-8 octets that represent the character. Although %HH-escaping of other encodings has been used in the past, it is no longer used today. This is quite independent of the encoding of the document itself.

How do I escape a Unicode string with Ruby?

I need to encode/convert a Unicode string to its escaped form, with backslashes. Anybody know how?
In Ruby 1.8.x, String#inspect may be what you are looking for, e.g.
>> multi_byte_str = "hello\330\271!"
=> "hello\330\271!"
>> multi_byte_str.inspect
=> "\"hello\\330\\271!\""
>> puts multi_byte_str.inspect
"hello\330\271!"
=> nil
In Ruby 1.9 if you want multi-byte characters to have their component bytes escaped, you might want to say something like:
>> multi_byte_str.bytes.to_a.map(&:chr).join.inspect
=> "\"hello\\xD8\\xB9!\""
In both Ruby 1.8 and 1.9 if you are instead interested in the (escaped) unicode code points, you could do this (though it escapes printable stuff too):
>> multi_byte_str.unpack('U*').map{ |i| "\\u" + i.to_s(16).rjust(4, '0') }.join
=> "\\u0068\\u0065\\u006c\\u006c\\u006f\\u0639\\u0021"
To use a unicode character in Ruby use the "\uXXXX" escape; where XXXX is the UTF-16 codepoint. see http://leejava.wordpress.com/2009/03/11/unicode-escape-in-ruby/
If you have Rails kicking around you can use the JSON encoder for this:
require 'active_support'
x = ActiveSupport::JSON.encode('µ')
# x is now "\u00b5"
The usual non-Rails JSON encoder doesn't "\u"-ify Unicode.
There are two components to your question as I understand it: Finding the numeric value of a character, and expressing such values as escape sequences in Ruby. Further, the former depends on what your starting point is.
Finding the value:
Method 1a: from Ruby with String#dump:
If you already have the character in a Ruby String object (or can easily get it into one), this may be as simple as displaying the string in the repl (depending on certain settings in your Ruby environment). If not, you can call the #dump method on it. For example, with a file called unicode.txt that contains some UTF-8 encoded data in it – say, the currency symbols €£¥$ (plus a trailing newline) – running the following code (executed either in irb or as a script):
s = File.read("unicode.txt", :encoding => "utf-8") # this may be enough, from irb
puts s.dump # this will definitely do it.
... should print out:
"\u20AC\u00A3\u00A5$\n"
Thus you can see that € is U+20AC, £ is U+00A3, and ¥ is U+00A5. ($ is not converted, since it's straight ASCII, though it's technically U+0024. The code below could be modified to give that information, if you actually need it. Or just add leading zeroes to the hex values from an ASCII table – or reference one that already does so.)
(Note: a previous answer suggested using #inspect instead of #dump. That sometimes works, but not always. For example, running ruby -E UTF-8 -e 'puts "\u{1F61E}".inspect' prints an unhappy face for me, rather than an escape sequence. Changing inspect to dump, though, gets me the escape sequence back.)
Method 1b: with Ruby using String#encode and rescue:
Now, if you're trying the above with a larger input file, the above may prove unwieldy – it may be hard to even find escape sequences in files with mostly ASCII text, or it may be hard to identify which sequences go with which characters. In such a case, one might replace the second line above with the following:
encodings = {} # hash to store mappings in
s.split("").each do |c| # loop through each "character"
begin
c.encode("ASCII") # try to encode it to ASCII
rescue Encoding::UndefinedConversionError # but if that fails
encodings[c] = $!.error_char.dump # capture a dump, mapped to the source character
end
end
# And then print out all the captured non-ASCII characters:
encodings.each do |char, dumped|
puts "#{char} encodes to #{dumped}."
end
With the same input as above, this would then print:
€ encodes to "\u20AC".
£ encodes to "\u00A3".
¥ encodes to "\u00A5".
Note that it's possible for this to be a bit misleading. If there are combining characters in the input, the output will print each component separately. For example, for input of 🙋🏾 ў ў, the output would be:
🙋 encodes to "\u{1F64B}".
🏾 encodes to "\u{1F3FE}".
ў encodes to "\u045E".
у encodes to "\u0443". ̆
encodes to "\u0306".
This is because 🙋🏾 is actually encoded as two code points: a base character (🙋 - U+1F64B), with a modifier (🏾, U+1F3FE; see also). Similarly with one of the letters: the first, ў, is a single pre-combined code point (U+045E), while the second, ў – though it looks the same – is formed by combining у (U+0443) with the modifier ̆ (U+0306 - which may or may not render properly, including on this page, since it's not meant to stand alone). So, depending on what you're doing, you may need to watch out for such things (which I leave as an exercise for the reader).
Method 2a: from web-based tools: specific characters:
Alternatively, if you have, say, an e-mail with a character in it, and you want to find the code point value to encode, if you simply do a web search for that character, you'll frequently find a variety of pages that give unicode details for the particular character. For example, if I do a google search for ✓, I get, among other things, a wiktionary entry, a wikipedia page, and a page on fileformat.info, which I find to be a useful site for getting details on specific unicode characters. And each of those pages lists the fact that that check mark is represented by unicode code point U+2713. (Incidentally, searching in that direction works well, too.)
Method 2b: from web-based tools: by name/concept:
Similarly, one can search for unicode symbols to match a particular concept. For example, I searched above for unicode check marks, and even on the Google snippet there was a listing of several code points with corresponding graphics, though I also find this list of several check mark symbols, and even a "list of useful symbols" which has a bunch of things, including various check marks.
This can similarly be done for accented characters, emoticons, etc. Just search for the word "unicode" along with whatever else you're looking for, and you'll tend to get results that include pages that list the code points. Which then brings us to putting that back into ruby:
Representing the value, once you have it:
The Ruby documentation for string literals describes two ways to represent unicode characters as escape sequences:
\unnnn Unicode character, where nnnn is exactly 4 hexadecimal digits ([0-9a-fA-F])
\u{nnnn ...} Unicode character(s), where each nnnn is 1-6 hexadecimal digits ([0-9a-fA-F])
So for code points with a 4-digit representation, e.g. U+2713 from above, you'd enter (within a string literal that's not in single quotes) this as \u2713. And for any unicode character (whether or not it fits in 4 digits), you can use braces ({ and }) around the full hex value for the code point, e.g. \u{1f60d} for 😍. This form can also be used to encode multiple code points in a single escape sequence, separating characters with whitespace. For example, \u{1F64B 1F3FE} would result in the base character 🙋 plus the modifier 🏾, thus ultimately yielding the abstract character 🙋🏾 (as seen above).
This works with shorter code points, too. For example, that currency character string from above (€£¥$) could be represented with \u{20AC A3 A5 24} – requiring only 2 digits for three of the characters.
You can directly use unicode characters if you just add #Encoding: UTF-8 to the top of your file. Then you can freely use ä, ǹ, ú and so on in your source code.
try this gem. It converts Unicode or non-ASCII punctuation and symbols to nearest ASCII punctuation and symbols
https://github.com/qwuen/punctuate
example usage:
"100٪".punctuate
=> "100%"
the gem uses the reference in https://lexsrv3.nlm.nih.gov/LexSysGroup/Projects/lvg/current/docs/designDoc/UDF/unicode/DefaultTables/symbolTable.html for the conversion.

Least used delimiter character in normal text < ASCII 128

For coding reasons which would horrify you (I'm too embarrassed to say), I need to store a number of text items in a single string.
I will delimit them using a character.
Which character is best to use for this, i.e. which character is the least likely to appear in the text? Must be printable and probably less than 128 in ASCII to avoid locale issues.
I would choose "Unit Separator" ASCII code "US": ASCII 31 (0x1F)
In the old, old days, most things were done serially, without random access. This meant that a few control codes were embedded into ASCII.
ASCII 28 (0x1C) File Separator - Used to indicate separation between files on a data input stream.
ASCII 29 (0x1D) Group Separator - Used to indicate separation between tables on a data input stream (called groups back then).
ASCII 30 (0x1E) Record Separator - Used to indicate separation between records within a table (within a group). These roughly map to a tuple in modern nomenclature.
ASCII 31 (0x1F) Unit Separator - Used to indicate separation between units within a record. The roughly map to fields in modern nomenclature.
Unit Separator is in ASCII, and there is Unicode support for displaying it (typically a "us" in the same glyph) but many fonts don't display it.
If you must display it, I would recommend displaying it in-application, after it was parsed into fields.
Assuming for some embarrassing reason you can't use CSV I'd say go with the data. Take some sample data, and do a simple character count for each value 0-127. Choose one of the ones which doesn't occur. If there is too much choice get a bigger data set. It won't take much time to write, and you'll get the answer best for you.
The answer will be different for different problem domains, so | (pipe) is common in shell scripts, ^ is common in math formulae, and the same is probably true for most other characters.
I personally think I'd go for | (pipe) if given a choice but going with real data is safest.
And whatever you do, make sure you've worked out an escaping scheme!
When using different languages, this symbol: ¬
proved to be the best. However I'm still testing.
Probably | or ^ or ~ you could also combine two characters
You said "printable", but that can include characters such as a tab (0x09) or form feed (0x0c). I almost always choose tabs rather than commas for delimited files, since commas can sometimes appear in text.
(Interestingly enough the ascii table has characters GS (0x1D), RS (0x1E), and US (0x1F) for group, record, and unit separators, whatever those are/were.)
If by "printable" you mean a character that a user could recognize and easily type in, I would go for the pipe | symbol first, with a few other weird characters (# or ~ or ^ or \, or backtick which I can't seem to enter here) as a possibility. These characters +=!$%&*()-'":;<>,.?/ seem like they would be more likely to occur in user input. As for underscore _ and hash # and the brackets {}[] I don't know.
How about you use a CSV style format? Characters can be escaped in a standard CSV format, and there's already a lot of parsers already written.
Can you use a pipe symbol? That's usually the next most common delimiter after comma or tab delimited strings. It's unlikely most text would contain a pipe, and ord('|') returns 124 for me, so that seems to fit your requirements.
For fast escaping I use stuff like this:
say you want to concatinate str1, str2 and str3
what I do is:
delimitedStr=str1.Replace("#","#a").Replace("|","#p")+"|"+str2.Replace("#","#a").Replace("|","#p")+"|"+str3.Replace("#","#a").Replace("|","#p");
then to retrieve original use:
splitStr=delimitedStr.Split("|".ToCharArray());
str1=splitStr[0].Replace("#p","|").Replace("#a","#");
str2=splitStr[1].Replace("#p","|").Replace("#a","#");
str3=splitStr[2].Replace("#p","|").Replace("#a","#");
note: the order of the replace is important
its unbreakable and easy to implement
Pipe for the win! |
We use ascii 0x7f which is pseudo-printable and hardly ever comes up in regular usage.
Well it's going to depend on the nature of your text to some extent but a vertical bar 0x7C doesn't crop up in text very often.
I don't think I've ever seen an ampersand followed by a comma in natural text, but you can check the file first to see if it contains the delimiter, and if so, use an alternative. If you want to always be able to know that the delimiter you use will not cause a conflict, then do a loop checking the file for the delimiter you want, and if it exists, then double the string until the file no longer has a match. It doesn't matter if there are similar strings because your program will only look for exact delimiter matches.
This can be good or bad (usually bad) depending on the situation and language, but keep mind mind that you can always Base64 encode the whole thing. You then don't have to worry about escaping and unescaping various patterns on each side, and you can simply seperate and split strings based on a character which isn't used in your Base64 charset.
I have had to resort to this solution when faced with putting XML documents into XML properties/nodes. Properties can't have CDATA blocks in them at all, and nodes escaped as CDATA obviously cannot have further CDATA blocks inside that without breaking the structure.
CSV is probably a better idea for most situations, though.
Both pipe and caret are the obvious choices. I would note that if users are expected to type the entire response, caret is easier to find on any keyboard than is pipe.
I've used double pipe and double caret before. The idea of a non printable char works if your not hand creating or modifying the file. For quick random access file storage and retrieval field width is used. You don't even have to read the file.. your literally pulling from the file by reference. This is how databases do some storage.. but they also manage the spaces between records and such. And it introduced the problem of max data element width. (Index attach a header which is used to define the width of each element and it's data type in the original old days.. later they introduced compression with remapping chars. This allows for a text file to get about 1/8 the size in transmission.. variable length char encoding for the win
make it dynamic : )
announce your control characters in the file header
for example
delimiter: ~
escape: \
wrapline: $
width: 19
hello world~this i$
s \\just\\ a sampl$
e text~$someVar$~h$
ere is some \~\~ma$
rkdown strikethrou$
gh\~\~ text
would give the strings
hello world
this is \just\ a sample text
$someVar$
here is some ~~markdown strikethrough~~ text
i have implemented something similar:
a plaintar text container format,
to escape and wrap utf16 text in ascii,
as an alternative to mime multipart messages.
see https://github.com/milahu/live-diff-html-editor

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