I'm trying to extract only certain elements of a string using regular expressions and I want to end up with only the captured groups.
For example, I'd like to run something like (is|a) on a string like "This is a test" and be able to return only "is is a". The only way I can partially do it now is if I find the entire beginning and end of the string but don't capture it:
.*?(is|a).*? replaced with $1
However, when I do this, only the characters preceding the final found/captured group are eliminated--everything after the last found group remains.
is is a test.
How can I isolate and replace only the captured strings (so that I end up with "is is a"), in both PHP and Perl?
Thanks!
Edit:
I see now that it's better to use m// rather than s///, but how can I apply that to PHP's preg_match? In my real regex I have several captured group, resulting in $1, $2, $3 etc -- preg_match only deals with one captured group, right?
If all you want are the matches, the there is no need for the s/// operator. You should use m//. You might want to expand on your explanation a little if the example below does not meet your needs:
#!/usr/bin/perl
use strict;
use warnings;
my $text = 'This is a test';
my #matches = ( $text =~ /(is|a)/g );
print "#matches\n";
__END__
C:\Temp> t.pl
is is a
EDIT: For PHP, you should use preg_match_all and specify an array to hold the match results as shown in the documentation.
You can't replace only captures. s/// always replaces everything included in the match. You need to either capture the additional items and include them in the replacement or use assertions to require things that aren't included in the match.
That said, I don't think that's what you're really asking. Is Sinan's answer what you're after?
You put everything into captures and then replaces only the ones you want.
(.*?)(is|a)(.*?)
Related
I would like to get a string made of one word with a delimiter word before and after it
i tried but doen t work
$stringData2 = file_get_contents('testtext3.txt');
$regular2=('/(?<=first del)*MAIN WORD(?=last del)*\s');
preg_match_all($regular2,
$stringData2,
$out, PREG_PATTERN_ORDER);
thank you very much for any help
No quantifier needed, add delimeter at end, put \s inside lookahead.
'/(?<=first del)MAIN WORD(?=last del\s)/'
This regex
(?<=xx)[^\s]*(?=yy)
matches hello in:
xxhelloyy
but fails to match in:
xxhello worldyy
This is probably what you're looking for.
If you want the delimiter string included in the match, then you should not be using lookahead or look or look behind. It should be something rather basic, like this.
/\s?first del MAIN WORD last del\s?/
If you do want to return JUST the MAIN WORD part of the match, then this will work.
/(?<=\s?first del)MAIN WORD(?=last del\s?)/
Put a 'i' at the very end of that to make it case insensitive, if you want. I only mention this, because in the example you gave me above has different case between the example text and the desired response.
<a href="/search?hl=en&pwst=1&sa=X&ei=RCPqTqkHycryA_bK_f0J&ved=0CCUQvwUoAQ&q=psychology&spell=1" class=spell><b><i>psychology</i></b></a>
Hi, I'm looking to create a regex which matches this anchor and returns the inner text of it.
This is what I've been trying as a regex but without success.
'/<a[^>]+class=\"spell\"[^>]*>(.*?)<\/a>/isU'
It's probably something really silly. Thanks.
Problem was missing quotes surrounding the class. Not proper html markup but I neglected to notice so I just changed my regex to have quotes as optional.
Final regex:
'/<a[^>]+class=\"?spell\"?[^>]*>(.*?)<\/a>/is'
The regex looks OK, although you don't need to escape the quotes. Perhaps PHP doesn't like it if you use unnecessary escapes, although I doubt it. The problem is more likely the way you're using the regex. Did you access group number 1?
if (preg_match('%<a[^>]+class="spell"[^>]*>(.*?)</a>%', $subject, $regs)) {
$result = $regs[1];
}
Your problem might be the combination of (.*?) and /isU modifier. That U alters the meaning of ? making your match group (.*) greedy actually. Then you will match parts beyond the <\/a> end marker, until it encounters another.
If you remove the /U it works as expected. With your given input text, at least.
Here are two options to fix your expression:
For starters, you can simplify your expression to:
class=\"spell\"[^>]*>(.*?)<\/a>
This captures
<b><i>psychology</i></b>
in Group 1. I assume this is what you want to achieve.
Then, if you want to capture "psychology" without the bold and italic tags, you can use:
class=\"spell\"[^>]*>\s*<(\w+)>?\s*<(\w+)>?\s*(.*?)<\/\2>\s*<\/\1>\s*<\/a>
This captures "psychology" in group 3.
In group 1, you will find the first optional tag, whether it be "b", "strong" or nothing.
In group 2, you will find the second optional tag, which was "i" in your example.
The multiple instances of \s* allow for optional space between the tags.
Is this what you were looking for?
I need a regular expression for php that outputs everything between <!--:en--> and <!--:-->.
So for <!--:en-->STRING<!--:--> it would output just STRING.
EDIT: oh and the following <!--:--> nedds to be the first one after <!--:en--> becouse there are more in the text..
The one you want is actually not too complicated:
/<!--:en-->(.*?)<!--:-->/gi
Your matches will be in capture group 1.
Explanation:
The .*? is a lazy quantifier. Basically, it means "keep matching until you find the shortest string that will still fit this pattern." This is what will cause the matching to stop at the first instance of <!--:-->, rather than sucking up everything until the last <!--:--> in the document.
Usage is something like preg_match("/<!--:en-->(.*?)<!--:-->/gi", $input) if I recall my PHP correctly.
If you have just that input
$input = '<!--:en-->STRING<!--:-->';
You can try with
$output = strip_tags($input);
Try:
^< !--:en-- >(.*)< !--:-- >$
I don't think any of the other characters need to be escaped.
<!--:en--\b[^>]*>(.*?)<!--:-->
This will match the things between your tags. This will break if you nest your tags, but you didnt say you were doing that :)
I am trying to pull the anchor text from a link that is formatted this way:
<h3><b>File</b> : i_want_this</h3>
I want only the anchor text for the link : "i_want_this"
"variable_text" varies according to the filename so I need to ignore that.
I am using this regex:
<a href=\"\/en\/browse\/file\/variable_text\">(.*?)<\/a>
This is matching of course the complete link.
PHP uses a pretty close version to PCRE (PERL Regex). If you want to know a lot about regex, visit perlretut.org. Also, look into Regex generators like exspresso.
For your use, know that regex is greedy. That means that when you specify that you want something, follwed by anything (any repetitions) followed by something, it will keep on going until that second something is reached.
to be more clear, what you want is this:
<a href="
any character, any number of times (regex = .* )
">
any character, any number of times (regex = .* )
</a>
beyond that, you want to capture the second group of "any character, any number of times". You can do that using what are called capture groups (capture anything inside of parenthesis as a group for reference later, also called back references).
I would also look into named subpatterns, too - with those, you can reference your choice with a human readable string rather than an array index. Syntax for those in PHP are (?P<name>pattern) where name is the name you want and pattern is the actual regex. I'll use that below.
So all that being said, here's the "lazy web" for your regex:
<?php
$str = '<h3><b>File</b> : i_want_this</h3>';
$regex = '/(<a href\=".*">)(?P<target>.*)(<\/a>)/';
preg_match($regex, $str, $matches);
print $matches['target'];
?>
//This should output "i_want_this"
Oh, and one final thought. Depending on what you are doing exactly, you may want to look into SimpleXML instead of using regex for this. This would probably require that the tags that we see are just snippits of a larger whole as SimpleXML requires well-formed XML (or XHTML).
I'm sure someone will probably have a more elegant solution, but I think this will do what you want to done.
Where:
$subject = "<h3><b>File</b> : i_want_this</h3>";
Option 1:
$pattern1 = '/(<a href=")(.*)(">)(.*)(<\/a>)/i';
preg_match($pattern1, $subject, $matches1);
print($matches1[4]);
Option 2:
$pattern2 = '()(.*)()';
ereg($pattern2, $subject, $matches2);
print($matches2[4]);
Do not use regex to parse HTML. Use a DOM parser. Specify the language you're using, too.
Since it's in a captured group and since you claim it's matching, you should be able to reference it through $1 or \1 depending on the language.
$blah = preg_match( $pattern, $subject, $matches );
print_r($matches);
The thing to remember is that regex's return everything you searched for if it matches. You need to specify that only care about the part you've surrounded in parenthesis (the anchor text). I'm not sure what language you're using the regex in, but here's an example in Ruby:
string = 'i_want_this'
data = string.match(/<a href=\"\/en\/browse\/file\/variable_text\">(.*?)<\/a>/)
puts data # => outputs 'i_want_this'
If you specify what you want in parenthesis, you can reference it:
string = 'i_want_this'
data = string.match(/<a href=\"\/en\/browse\/file\/variable_text\">(.*?)<\/a>/)[1]
puts data # => outputs 'i_want_this'
Perl will have you use $1 instead of [1] like this:
$string = 'i_want_this';
$string =~ m/<a href=\"\/en\/browse\/file\/variable_text\">(.*?)<\/a>/;
$data = $1;
print $data . "\n";
Hope that helps.
I'm not 100% sure if I understand what you want. This will match the content between the anchor tags. The URL must start with /en/browse/file/, but may end with anything.
#(.*?)#
I used # as a delimiter as it made it clearer. It'll also help if you put them in single quotes instead of double quotes so you don't have to escape anything at all.
If you want to limit to numbers instead, you can use:
#(.*?)#
If it should have just 5 numbers:
#(.*?)#
If it should have between 3 and 6 numbers:
#(.*?)#
If it should have more than 2 numbers:
#(.*?)#
This should work:
<a href="[^"]*">([^<]*)
this says that take EVERYTHING you find until you meet "
[^"]*
same! take everything with you till you meet <
[^<]*
The paratese around [^<]*
([^<]*)
group it! so you can collect that data in PHP! If you look in the PHP manual om preg_match you will se many fine examples there!
Good luck!
And for your concrete example:
<a href="/en/browse/file/variable_text">([^<]*)
I use
[^<]*
because in some examples...
.*?
can be extremely slow! Shoudln't use that if you can use
[^<]*
You should use the tool Expresso for creating regular expression... Pretty handy..
http://www.ultrapico.com/Expresso.htm
i dont undestand the () in regexp.
eg. what is the difference between these lines:
"/hello/"
"/(hello)/"
() provide a way to capture matches and for grouping take a look here for a more full description.
By wrapping it in ( and ) you can capture it and handle it as a whole. Suppose we have the following text:
hellohello hello!
If I wanted to find the word "hello" in two's, I could do this:
/hellohello/
Or, I could do this:
/(hello){2}/
As you have written it, there is no actual difference between the two examples. But parantheses allow you to apply post-logic to that entire group of characters (e.g. as another poster used as an example, {2} afterwards would state the the string "hello" is typed two times in a row without anything in between - hellohello. Parantheses also allow you to use "or" statements - "/(hello|goodbye)/" would match EITHER hello OR goodbye.
The most powerful use of them however is extracting data from a string, rather than just matching it, it lets you pull the data out of the string and do what you want with it.
e.g. in PHP if you did
preg_replace( "/hello (.+)/i", "hello how are you?", $holder );`
Then $holder[1] will contain ALL the text after "hello ", which in this case would be "how are you?"