Replace part of string between quotes in php regex

Question

Now I've got very basic regex skills, only used regex a couple of times for basic stuff. This has probably been asked before, which I apologize for, but I couldn't find any answer for this. Found similar, though and tried to adapt it but to no avail. OK, to the question - How do I replace a space only between certain characters (doublequotes in this case)?

Say i have the following string:

"mission podcast" modcast A B C "D E F"

I want to replace the spaces between mission and podcast as well as the ones between D, E & F whilst leaving the other ones untouched.

P.S. What if space was a string? An example for that is welcome as well.

Edited this a bit I hope now it's more clear. Edit 2: I need to do this on a string in php and execute it in the shell. Edit 3: I'm sorry i changed the whole question 3 times it's just i'm getting quite confused myself. Cheers!

Answer 1

Description

I would attack this problem by first splitting the string into groups of either quoted or not quoted strings.

Then iterating through the matches and if Capture Group 1 is populated, then that string is quoted so just do a simple replace on replace Capture Group 0. If Capture group 1 is not populated then skip to the next match.

On each iteration, you'd want to simply build up a new string.

Since splitting the string is the difficult part, I'd use this regex:

("[^"]*")|[^"]*

Example

Sample Text

"mission podcast" modcast A B C "D E F"

Code

PHP Code Example: 
<?php
$sourcestring="your source string";
preg_match_all('/("[^"]*")|[^"]*/i',$sourcestring,$matches);
echo "<pre>".print_r($matches,true);
?>

Capture Groups

$matches Array:
(
    [0] => Array
        (
            [0] => "mission podcast"
            [1] =>  modcast A B C 
            [2] => "D E F"
            [3] => 
        )

    [1] => Array
        (
            [0] => "mission podcast"
            [1] => 
            [2] => "D E F"
            [3] => 
        )

)

PHP Example

This php script will replace only the spaces inside quoted strings.

Working example: http://ideone.com/jBytL3

Code

<?php

$text ='"mission podcast" modcast A B C "D E F"';

preg_match_all('/("[^"]*")|[^"]*/',$text,$matches);

foreach($matches[0] as $entry){
    echo preg_replace('/\s(?=.*?")/ims','~~new~~',$entry);
    }

Output

"mission~~new~~podcast" modcast A B C "D~~new~~E~~new~~F"

Answer 2

If you don't need to use regular expressions, here is an iterative version that works:

<?php
    function remove_quoted_whitespace($str) {
        $result = '';
        $length = strlen($str);
        $index = 0;
        $in_quotes = false;

        while ($index < $length) {
            $c = $str[$index++];

            if ($c == '"') {
                $in_quotes = !$in_quotes;
            } else if ($c == ' ') {
                if ($in_quotes) {
                    continue;
                }
            }

            $result .= $c;
        }

        return $result;
    }

    $input = '"mission podcast" modcast A B C "D E F"';
    $output = remove_quoted_whitespace($input);

    echo $input . "\n";
    echo $output . "\n";
?>

Answer 3

The entire foreach is not needed at all! It is possible to use a one-liner for this.

Here is the code which replaces spaces in quoted strings. The idea is that if a space is inside quotes, it is followed by odd number of quotes. It can be done by regexp look-ahead.

echo preg_replace('{\s+(?!([^"]*"[^"]*")*[^"]*$)}',"x",$str);

That's all! How it works? It matches all \s characters which are not followed by even number of quotes. The matching spaces get replaced by x. You can of course change it to any desired value or leave it empty.