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Why doesn't prag_match find "<a"?
Discuss Why doesn't prag_match find "<a"? in the Regex Programming forum on Dev Shed.
Why doesn't prag_match find "<a"? Regular expressions forum covering PCRE and POSIX techniques, practices, and standards. Regular expressions help shorten coding time by providing the ability to compact many lines of code into one string.
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November 30th, 2011, 03:34 PM
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Contributing User
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Why doesn't prag_match find "<a"?
Alright, I haven't done much regex in my work which hasn't really been needed in my projects and when it has I just copy and paste regex for what is needed. But I ran in to a simple problem when testing some regex and I'm wondering what is causing it. In php if I do this
PHP Code:
$word = "<a";
$pattern = '/<a/';
preg_match($pattern,$word,$matches);
print_r($matches);
This shows up as blank. If I change $word and $pattern to "<>" or "<" or "a" it will find a match.
Is there something special about the "<" symbol in regex?
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November 30th, 2011, 04:21 PM
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Still alive
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Join Date: Mar 2007
Location: Washington, USA
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If I run that exact code I get the right results...
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November 30th, 2011, 05:17 PM
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Contributing User
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Quote: | Originally Posted by requinix If I run that exact code I get the right results... |
That's what I don't understand. Can you think of anything that can be causing this in my configuration? I've tried it 50 times and $matches shows up empty. If I try any of those other combinations I get the right result.
It only happens if I have a "<" that starts off the prag_match. If I do "<a>" it shows up blank also. But if I do "<>" it will find a match. Any thoughts?
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November 30th, 2011, 06:26 PM
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Still alive
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Join Date: Mar 2007
Location: Washington, USA
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Are you saying you've tried the code you posted, character for character, and are getting bad results? What's your exact code?
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November 30th, 2011, 06:29 PM
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Contributing User
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Yea, this is definitely weird. It has something to do with the "<". I also tried the following and one matches the whole string and the other matches just the first letter.
PHP Code:
$word = "a<b>";
$pattern = "/a<b>/";
preg_match($pattern,$word,$matches);
print_r($matches);
//Array shows up Array([0]=> a)
So that just reads the letter a
If I do this, it shows up with a correct match
PHP Code:
$word = "ab>";
$pattern = "/ab>/";
preg_match($pattern,$word,$matches);
print_r($matches);
//Array shows up Array([0]=> ab>)
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November 30th, 2011, 06:31 PM
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Contributing User
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Quote: | Originally Posted by requinix Are you saying you've tried the code you posted, character for character, and are getting bad results? What's your exact code? |
That is my exact code. I have tried it every way possible, and it shows up blank every time.
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November 30th, 2011, 06:54 PM
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Still alive
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Join Date: Mar 2007
Location: Washington, USA
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...
You are looking at the HTML source of the page, right?
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November 30th, 2011, 07:11 PM
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Contributing User
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Quote: | Originally Posted by requinix ...
You are looking at the HTML source of the page, right? |
Ahhhh... I am an idiot, lol!!
Thanks requinix
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December 19th, 2011, 05:27 PM
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Turn left at the third duck
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Join Date: Dec 2011
Location: Nelson, NZ
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To complete the answer in case someone else is on the same track. This is a common phenomenon when pregmatching html and outputting it to the page to test the expression.
The easy fix is to use htmlentities.
So here, something like:
PHP Code:
echo htmlentities($matches)."<br />";
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December 20th, 2011, 08:26 AM
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Likely to be eaten by a grue.
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Join Date: Oct 2006
Location: Pennsylvania, USA
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$matches is an array in this case, so you'll have to use:
PHP Code:
echo htmlentities(print_r($matches,1))."<br />\n";
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December 20th, 2011, 11:19 PM
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Turn left at the third duck
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Join Date: Dec 2011
Location: Nelson, NZ
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Spot on.
Thanks for pointing that out, I didn't pay enough attention to the details. 
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