Getting too many matches with my regex?

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April 23rd, 2012, 11:11 PM

jusserfinn

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PHP - Getting too many matches with my regex?

I'm fairly new with PHP and regex's. I am attempting to match the pattern: word-word 1 or more times in a file. my code:

Code:

 <?php

$fIn = fopen( 'matchtext.dat', 'r' );
if( ! $fIn )
     die( "Couldn't open the source file for reading<br/>");

while( $line = fgets( $fIn ) )
     if( preg_match( '|\b([a-zA-Z]+-+)+[a-zA-Z]+|', $line, $matches ) ) {
            echo "<pre>"; print_r( $matches ); echo "</pre>";
     }

?>

is returning an additional array entry which is the next-to-the-last word in the line with a hyphen :
Array
(
[0] => learn-english-today
[1] => english-
)
Array
(
[0] => that-than-which-nothing-greater-can-be-though
[1] => be-
)
Array
(
[0] => that-than-which-nothing-greater-can-be-thought
[1] => be-
)

Where did I go wrong? I only want the first!

April 23rd, 2012, 11:50 PM

E-Oreo

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Quote:

... $matches[1] will have the text that matched the first captured parenthesized subpattern, and so on.

source

([a-zA-Z]+-+) is a parenthesized subpattern. However, the parenthesis are an essential part of your regex so you cannot remove them. If you only want the first element in the array then only use the first and just ignore the second.

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April 24th, 2012, 12:09 AM

jusserfinn

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Quote:

Originally Posted by E-Oreo

If you only want the first element in the array then only use the first and just ignore the second.

Thanks:
Do you mean the "[a-zA-Z]+|"? If so, that won't work because then it will find trailing hyphens (that-than-which-nothing-greater-can-be-)

the second part in this case needs to find a final word after the last hyphen.

April 25th, 2012, 02:21 AM

abareplace

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Hi, jusserfinn,

the subexpression [a-zA-Z]+-+ is captured several times. For example, in "learn-english-today", it will capture "learn-", then "english-". Only the last captured string (english-) will be saved.

If you want to match the first word, use

Code:

<?php

if( preg_match( '|\b([a-zA-Z]+)(?:-[a-zA-Z]+)+|', 'learn-english-today', $matches ) ) {
            echo "<pre>"; print_r( $matches ); echo "</pre>";
     }

?>

April 25th, 2012, 04:40 PM

jusserfinn

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Ok, I know there is something to be said about looking up your question in the manual (which I did), but loads more should be said about checking it twice!

PHP.net says:

Code:

int preg_match ( string $pattern , string $subject [, array &$matches [, int $flags = 0 [, int $offset = 0 ]]] )

"If matches is provided, then it is filled with the results of search. $matches[0] will contain the text that matched the full pattern, $matches[1] will have the text that matched the first captured parenthesized subpattern, and so on."

So simple, I must have skimmed over it.

I fixed my code by adding [0] to the $matches in the echo statement:

Code:

 <?php

$fIn = fopen( 'matchtext.dat', 'r' );
if( ! $fIn )
     die( "Couldn't open the source file for reading<br/>");

while( $line = fgets( $fIn ) )
       if( preg_match( '|\b([a-zA-Z]+-+)+[a-zA-Z]+|', $line, $matches ) ) {
                echo "<pre>"; print_r( $matches[0] ); echo "</pre>";
     }
?>

Thanks for trying though!