I've hit a snag in a syntax highlighter I've been working on. PHP supports strings contained between both "" and ''. Unlike C#, which is more easily controlled by only allowing "", with the option # for automatically escaping the string.
If I have two strings, like so:
$code = "print( \"<div class='test'>content?div><div class='test'>content</div>\" );";
If I echo $code, I will get:
print( "<div class='test'>content?div><div class='test'>content</div>" );
Here's my problem. When I parse content between the starting quote and ending quote, I removed such content to be put back later (so I don't cross highlight), using a clipboard tool (just copy paste). I have it setup to parse content between '' first using regex. The end result (after both string types) will look like so:
print( "<div class=>content?div><div class=>content</div>" );
How can I modify my regex to look back (from start) and forward (from end) to look for the topmost string delimeter (' or "). It's hard to explain, hopefully someone gets it, otherwise I'll just have to live with it.
This is not possible with regular expressions; they are not powerful enough to deal with recursion. They cannot close nested parentheses correctly, they cannot close nested quotes correctly. You need a push-down automata (or a context-free language) at the least for this kind of functionality.
Related
I need to scrape some data from a website. For that I am using preg_match, but I am not able to write the regex for it. The data on the website is
title="Russia"/></a>
<small>*</small> <a href="/profile/roman
I have written the regex as #title=\"Russia\"\/><\/a>((\n|\r)*)<small>*<\/small> <a href=\"/profile/(.+?)\"#sx
But this is not working and I dont know why ? When I echo my regex it says #title="Russia"\/><\/a>(( | )*)*<\/small> . Where are the others gone? And why is it not working ?
Try this:
#title=\"Russia\"/></a>(\s*)<small>\*</small>\s+<a\s+href=\"/profile/(.+?)\"#sx
I have escaped the * because its a metacharacter. Without it, you would match strings containing the word small followed by zero or more >s.
You really should not use regexes to evaluate markup content, especially when you acquire it by scrapping pages.
In your case there are at least three reasons that might be responsible for breaking your regex.
Do not attempt to write your own whitespace evaluators when you can simply use \s which stands for "any whitespace character"
In regular expressions asterisk (*) has a special meaning which is why you can't simply use it to identify asterisks. If you want to collect content inside the small attribute you should use <small>(.*)</small> instead. If on the other hand you are actually expecting an asterisk then you have to escape it like this <small>\*</small>.
Your regex expects a closing quote for your href attribute on that last <a> but in your sample markup you have none. Provided that on the original page you do have a closing quote the following regex should do the trick.
#title=\"Russia\"\/><\/a>(\s*)<small>\*</small> <a href="/profile/(.+)?\"#sx
However once again I have to advise using a DOM parser like DOMDocument for this not only because it is much more reliable when handling markup content but also because it can interpret bad markup as well (if its loaded as HTML of course).
I'm looking for a regex that will scan a document to match a function call, and return the value of the first parameter (a string literal) only.
The function call could look like any of the following:
MyFunction("MyStringArg");
MyFunction("MyStringArg", true);
MyFunction("MyStringArg", true, true);
I'm currently using:
$pattern = '/Use\s*\(\s*"(.*?)\"\s*\)\s*;/';
This pattern will only match the first form, however.
Thanks in advance for your help!
Update
I was able to solve my problem with:
$pattern = '/Use\s*\(\s*"(.*?)\"/';
Thanks Justin!
~Scott
If you only care about the value of the first parameter, you can just chop off the end of the regex:
$pattern = '/Use\s*\(\s*"(.*?)\"/';
However, you should understand that this (or any pure-regex solution for this problem) will not be perfect, and there will be some possible cases it handles incorrectly. In this case, you'll get false positives, and escaped quotes (\") will break it.
You can ignore escaped quotes by complicating it a bit:
$pattern = '/Use\s*\(\s*"(.*?)(?!<(?:\\\\)*\\)\"/';
This ignores " characters inside the quoted string if they have an odd number of backslashes in front of them.
However, the false-postives issue can't be helped without introducing false-negatives, and vice versa. This is because PHP is an irregular language, so it can't be parsed with "pure" regex, and even modern regex engines that allow recursion are going to need some pretty complex code to do a really thorough job at this.
All I'm saying is, if you're planning a one-off job to quickly scrape through some PHP you wrote yourself, regex is probably fine. If you're looking for something robust and open-ended that will do this on arbitrary PHP code, you need some kind of reflection or PHP parser.
This might be slightly simpler, though will only work if you have double quotes and not single quotes:
$pattern = /Use\s*[^\"]*\"([^\"]*)\"/
OK, I need to scan many HTML / XHTML documents to see if a particular file has been embedded with SWFObject. If it's the case, I need to replace the call to something else.
So far I have extracted the <script> contents where the calls can be made. Now I need to scan this string to check if the call is there and if it's there I need to replace it.
I know this is a bit odd, but the content comes from a third party which we don't have control on.
Since the call can be made in many different syntax, I will need a regular expression to find and replace the calls.
OK imagine the following scenario:
I'm searching if the file test.swf is embedded with SWFObject in the file.
The <script> content look like this:
alert('test.swf');
//some other random stuff here
swfobject.embedSWF("test.swf",
"The alternative content can screw the regexp with );", "300", "120",
"9.0.0", false, flashvars, params, attributes);
Now I would like to replace swfobject.embedSWF (and all parameters) to something else.
Is there a not too horrible way to do this? Don't forget that the call can be on one or many lines, that the parameters can be wrapped with single quotes (') or double quotes ("), that whitespace can be all around...
EDIT: OK since catching all kind of JS syntax is a bit overkill I will simplify the requirement:
The regular expression can assume only the following
The call is always on the same line
It always start with swfobject.embedSWF (case sensitive)
Is then followed (or not) by whitespaces and then a (
Is then followed (or not) by whitespaces and then a " or a ' (either one but one of the 2 is required)
Is then followed by the filename
Is then followed by " or ' (if we can ensure that it's the same char that in 4 good if not too bad)
Is then followed (or not) by whitespaces and then a ,
Is then followed by anything
Is then followed by ) then any whitespaces (or not) then ; then an end of line.
It should be much simpler to parse this way (I guess).
EDIT 2: I've cooked a solution. I think I'm close but it's not working, Anyone can help? 0 should match but it's not...
<?php
$myFilename = 'test.swf';
$testCases = array();
$testCases[] = 'swfobject.embedSWF("test.swf", "The alternative content can screw the regexp with );", "300", "120", "9.0.0", false, flashvars, params, attributes);';
foreach ($testCases as $i => $currTest)
{
$currResult = preg_match('/\s*swfobject\.embedSWF\s*\(\s*(["\'])(' . preg_quote($myFilename) . ')[^"\']+\1\s*,[\s\S]+?\)\s*;\s*$/', $currTest);
if ($currResult === false || $currResult < 1)
echo $i, ' Not matching', PHP_EOL;
else
echo $i, ' Matching', PHP_EOL;
}
?>
Well, somebody had the time to write a basic javascript parser in PHP. I'd give the tokenizer a try (possibly using an HTML parser to first find the <script> nodes).
In regards of your EDIT2...
I'm not the best with regular expressions but you can try:
$currResult = preg_match('/\s*swfobject\.embedSWF\s*\(\s*(["\'])(' . preg_quote($myFilename) . ')\1\s*,[\s\S]+?\)\s*;\s*$/', $currTest);
Seems to work OK for me.
Use 'grep' or similar on the command line to get a list of files that contain the .swf/script/object strings you need. That'll whittle down the number of files you need to process.
Then, use a PHP script to slurp each of those files into the DOM parser of your choice and do the replacing/fixing-up there.
I'm trying to write a regular expression using the PCRE library in PHP.
I need a regex to match only &, > and < chars that exist within string part of any XML node and not the tag declaration themselves.
Input XML:
<pnode>
<cnode>This string contains > and < and & chars.</cnode>
</pnode>
The idea is to to a search and replace these chars and convert them to XML entities equivalents.
If I was to convert the entire XML to entities the XML would look like this:
Entire XML converted to entities
<pnode>
<cnode>This string contains > and < and & chars.</cnode>
</pnode>
I need it to look like this:
Correct XML
<pnode>
<cnode>This string contains > and < and & chars.</cnode>
</pnode>
I have tried to write a regular expression to match these chars using look-ahaead but I don't know enough to get this to work. My attempt (currently only attempting to match > symbols):
/>(?=[^<]*<)/g
Just to make it clear the XML I'm trying to fix comes from a 3rd party and they seem unable to fix it their end hence my attempt to fix it.
In the end I've opted to use the Tidy library in PHP. The code I used is shown below:
// Specify configuration
$config = array(
'input-xml' => true,
'show-warnings' => false,
'numeric-entities' => true,
'output-xml' => true);
$tidy = new tidy();
$tidy->parseFile('feed.xml', $config, 'latin1');
$tidy->cleanRepair()
This works perfectly correcting all the encoding errors and converting invalid characters to XML entities.
Classic example of garbage in, garbage out. The real solution is to fix the broken XML exporter, but obviously that's out of the scope of your problem. Sounds like you might have to manually parse the XML, run htmlentites() on the contents, then put the XML tags back.
I'm reasonably certain it's simply not possible. You need something that keeps track of nesting, and there's no way to get a regular expression to track nesting. Your choices are to fix the text first (when you probably can use an RE) or use something that's at least vaguely like an XML parser, specifically to the extent of keeping track of how the tags are nested.
There's a reason XML demands that these characters be escaped though -- without that, you can only guess about whether something is really a tag or not. For example, given something like:
<tag>Text containing < and > characters</tag>
you and I can probably guess that the result should be: ...containing < and >... but I'm pretty sure the XML specification allows the extra whitespace, so officially "< and >" should be treated as a tag. You could, I suppose, assume that anything that looks like an un-matched tag really isn't intended to be a tag, but that's going to take some work too.
Would it be possible to intercept the text before it tries to become part of your XML? A few ounces of prevention might be worth pounds of cure.
This should do it for ampersands:
/(\s+)(&)(\s+)/gim
This means you're only looking for those characters when they have whitespace characters on both sides.
Just make sure the replacement expression is "$1$2amp;$3";
The others would go like this, with their replacement expressions on the right
/(\s+)(>)(\s+)/gim "$1>$2"
/(\s+)(<)(\s+)/gim "$1<$2"
As stated by others, regular expressions don't do well with hierarchical data. Besides, if the data is improperly formatted, you can't guarantee that you'll get it right. Consider:
<xml>
<tag>Something<br/>Something Else</tag>
</xml>
Is that <br/> supposed to read <br/>? There's no way to know because it's validly formatted XML.
If you have arbitrary data that you wish to include in your XML tree, consider using a <![CDATA[ ... ]]> block instead. It's treated the same as a text node, and the only thing you don't have to escape is the character sequence ]]>.
What you have there is not, of course, XML. In XML, the characters '<' and '&' may not occur (unescaped) inside text: only inside a comment, CDATA section, or processing instruction. Actually, '>' can occur in text, except as part of the string ']]>'. In well-formed XML, literal '<' and '&' characters signal the start of markup: '<' signals the start of a start tag, end tag, or empty element tag, and '&' signals the start of an entity reference. In both these cases, the next character may NOT be whitespace. So using an RE like Robusto's suggestion would find all such occurrences. You might also need to catch corner cases like '<<', '<\', or '&<'. In this case you don't need to try to parse your input, an RE will work fine.
If the source contains strings like '<something ' where 'something' matches the production for a Name:
Name ::= NameStartChar (NameChar)*
Then you have more of a problem. You are going to have to (try to) parse your input as if it were real XML, and detect the error cases of malformed Names, non-matching start & end tags, malformed attributes, and undefined entity references (to name a few). Unfortunately the error condition isn't guaranteed to happen at the location of the error.
Your best bet may be to use an RE to catch 90% of the error and fix the rest manually. You need to look for a '<' or '&' followed by anything other than a NameStartChar
First things first: Neither this, this, this nor this answered my question. So I'll open a new one.
Please read
Okay okay. I know that regexes are not the way to parse general HTML. Please take note that the created documents are written using a limited, controlled HTML subset. And people writing the docs know what they're doing. They are all IT professionals!
Given the controlled syntax it is possible to parse the documents I have here using regexes.
I am not trying to download arbitrary documents from the web and parse them!
And if the parsing does fail, the document is edited, so it'll parse. The problem I am addressing here is more general than that (i.e. not replace patterns inside two other patterns).
A little bit of background (you can skip this...)
In our office we are supposed to "pretty print" our documentation. Hence why some came up with putting it all into Word documents. So far we're thankfully not quite there yet. And, if I get this done, we might not need to.
The current state (... and this)
The main part of the docs are stored in a TikiWiki database. I've created a daft PHP script which converts the documents from HTML (via LaTeX) to PDF. One of the must have features of the selected Wiki-System was a WYSIWYG editor. Which, as expected leaves us with documents with a less then formal DOM.
Consequently, I am transliterating the document using "simple" regexes. It all works (mostly) fine so far, but I encountered one problem I haven't figured out on my own yet.
The problem
Some special characters need to replaced by LaTeX markup. For exaple, the \ character should be replaced by $\backslash$ (unless someone knows another solution?).
Except while in a verbatim block!
I do replace <code> tags with verbatim sections. But if this code block contains backslashes (as is the case for Windows folder names), the script still replaces these backslashes.
I reckon I could solve this using negative LookBehinds and/or LookAheads. But my attempts did not work.
Granted, I would be better off with a real parser. In fact, it is something on my "in-brain-roadmap", but it is currently out of the scope. The script works well enough for our limited knowledge domain. Creating a parser would require me to start pretty much from scratch.
My attempt
Example Input
The Hello \ World document is located in:
<code>C:\documents\hello_world.txt</code>
Expected output
The Hello $\backslash$ World document is located in:
\begin{verbatim}C:\documents\hello_world.txt\end{verbatim}
This is the best I could come up with so far:
<?php
$patterns = array(
"special_chars2" => array( '/(?<!<code[^>]*>.*)\\\\[^$](?!.*<\/code>)/U', '$\\backslash$'),
);
foreach( $patterns as $name => $p ){
$tex_input = preg_replace( $p[0], $p[1], $tex_input );
}
?>
Note that this is only an excerpt, and the [^$] is another LaTeX requirement.
Another attempt which seemed to work:
<?php
$patterns = array(
"special_chars2" => array( '/\\\\[^$](?!.*<\/code>)/U', '$\\backslash$'),
);
foreach( $patterns as $name => $p ){
$tex_input = preg_replace( $p[0], $p[1], $tex_input );
}
?>
... in other words: leaving out the negative lookbehind.
But this looks more error-prone than with both lookbehind and lookahead.
A related question
As you may have noticed, the pattern is ungreedy (/.../U). So will this match only as little possible inside a <code> block? Considering the look-arounds?
If me, I will try to find HTML parser and will do with that.
Another option is will try to chunk the string into <code>.*?</code> and other parts.
and will update other parts, and will recombine it.
$x="The Hello \ World document is located in:\n<br>
<code>C:\documents\hello_world.txt</code>";
$r=preg_split("/(<code>.*?<\/code>)/", $x,-1,PREG_SPLIT_DELIM_CAPTURE);
for($i=0;$i<count($r);$i+=2)
$r[$i]=str_replace("\\","$\\backslash$",$r[$i]);
$x=implode($r);
echo $x;
Here is the results.
The Hello $\backslash$ World document is located in:
C:\documents\hello_world.txt
Sorry, If my approach is not suitable for you.
I reckon I could solve this using negative LookBehinds and/or LookAheads.
You reckon wrong. Regular expressions are not a replacement for a parser.
I would suggest that you pipe the html through htmltidy, then read it with a dom-parser and then transform the dom to your target output format. Is there anything preventing your from taking this route?
Parser FTW, ok. But if you can't use a parser, and you can be certain that <code> tags are never nested, you could try the following:
Find <code>.*?</code> sections of your file (probably need to turn on dot-matches-newlines mode).
Replace all backslashes inside that section with something unique like #?#?#?#
Replace the section found in 1 with that new section
Replace all backslashes with $\backslash$
Replace als <code> with \begin{verbatim} and all </code> with \end{verbatim}
Replace #?#?#?# with \
FYI, regexes in PHP don't support variable-length lookbehind. So that makes this conditional matching between two boundaries difficult.
Pandoc? Pandoc converts between a bunch of formats. you can also concatenate a bunch of flies together then covert them. Maybe a few shell scripts combined with your php scraping scripts?
With your "expected input" and the command pandoc -o text.tex test.html the output is:
The Hello \textbackslash{} World document is located in:
\verb!C:\documents\hello_world.txt!
pandoc can read from stdin, write to stdout or pipe right into a file.
Provided that your <code> blocks are not nested, this regex would find a backslash after ^ start-of-string or </code> with no <code> in between.
((?:^|</code>)(?:(?!<code>).)+?)\\
| | |
| | \-- backslash
| \-- least amount of anything not followed by <code>
\-- start-of-string or </code>
And replace it with:
$1$\backslash$
You'd have to run this regex in "singleline" mode, so . matches newlines. You'd also have to run it multiple times, specifying global replacement is not enough. Each replacement will only replace the first eligible backslash after start-of-string or </code>.
Write a parser based on an HTML or XML parser like DOMDocument. Traverse the parsed DOM and replace the \ on every text node that is not a descendent of a code node with $\backslash$ and every node that is a code node with \begin{verbatim} … \end{verbatim}.