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RegEx search for repeating hyphens

Posted on 2011-02-20
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Last Modified: 2012-05-11
I am trying to replace multiple hyphens with a single one. Here is my php code to achive this

<?php
  $string = "a--b---c-d-e";
  $newstring = preg_replace("/(-)(\1+)/", "-", $string);
?>

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I want the $newsting to be "a-b-c-d-e"

However, it does not do anything to the original string. Why is it not working?
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Question by:hvs69
4 Comments
 
LVL 27

Accepted Solution

by:
Lukasz Chmielewski earned 500 total points
ID: 34936129
Try
<?php
  $string = "a--b---c-d-e";
  $newstring = preg_replace("/[-]+/", "-", $string);
  echo"$newstring";
?>
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LVL 4

Expert Comment

by:LAMASE
ID: 34936273
i agree with @Roads. If you want something more general you can use

<?php
  $string = "a--b--  ## -c-d-..e(@)-g";
  $newstring = preg_replace("/[^a-z]+/", "-", $string);
  echo $newstring;
?>

this will eliminate everything between lowercase letters and puts a single hypen between..

This and @Roads solutions doesn't remove the trailing hypens: if you have

$string = '-a-b-';

it will keep as is. Do you need this too? You can do it in two easy steps (or in one with a more complex regexp)

<?php
  $string = "a--b---c-d-e";
  $newstring = preg_replace("/[^a-z]+/", " ", $string);
  $newstring = preg_replace("/ +/", "-", trim($string));
  echo"$newstring";
?>

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LVL 1

Expert Comment

by:jfk013097
ID: 34936869
ereg_replace("--*", "-", $string)

will replace all multiple instances of - with a single one
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LVL 111

Expert Comment

by:Ray Paseur
ID: 34937757
ereg functions are deprecated.

Regarding this, "it does not do anything to the original string." - that is correct, because the new value is assigned to the variable named $newstring.

http://www.laprbass.com/RAY_temp_hvs69.php

Outputs: a-b-c-d-e
<?php // RAY_temp_hvs69.php
error_reporting(E_ALL);

// TEST DATA FROM THE POST AT EE
$string = "a--b---c-d-e";

// CONSTRUCT A REGEX
$regex 
= '/'  // REGEX DELIMITER
. '-+' // MORE THAN ONE HYPHEN
. '/'  // REGEX DELIMITER
;

// REPLACE THE HYPHENS WITH ONE HYPHEN
$newstring = preg_replace($regex, '-', $string);
echo $newstring;

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