PHP: while loop - using the altered variable in the condition

Question

I have a while loop issue in PHP that seems like it could have been solved using the ampersand sign to make it a reference if it were elsewhere. Below is an example. I'm trying to append _n to the filename (in the basename). If there's _1 then I want it to be _2, if there's _2 I want it to be _3 and so on. For some reason I can't update the $filename variable in the condition so I think it's not getting changed in the loop.

$dir = 'images';
$filename = '123.jpg';
$i = 0;
while (file_exists($dir.'/'.$filename)) {
    $filename = preg_replace('/^(\d*?)(\.jpg)$/',"$1_".(++$i)."$2",$filename);
}
echo $filename;

What am I doing wrong?

Answer 1

It looks like your regex is a little off, and you are not capturing the _n if it already exists.

while (file_exists($dir.'/'.$filename)) {
  $filename = preg_replace('/^(\d+)(.*)(\.jpg)$/',"$1_".(++$i)."$3",$filename);
  //-------------------------------^^^^ Capture the _n if it exists
  // And stick the number in with $1 and $3 (now the .jog)
}
echo $filename;

// Current files...
123_1.jpg
123_2.jpg
123.jpg

// Outputs 123_3.jpg

Answer 2

If you didn't want to use a regex and you wanted to make sure you got all the jpg files in a directory you could use glob() and some basic string manipulation functions like so:

$dir = 'images/';
foreach (glob($dir.'*.jpg') as $file) {
  $ext = strpos($file, '.jpg'); // get index of the extension in string
  $num = (int) substr($file, 0, $ext); // get the numeric part
  $file = $num+1 . '.jpg'; // rebuild the file name
  echo $file, PHP_EOL;
}

Answer 3

Here's an example using a function and no regex. This way works for a much wider range of circumstances.

ie any file extension works, and, underscores or period allowed in the basename

If you don't need those things then using preg_replace() is cleaner, see Michael's answer.

<?php

function nextUnusedFileName($path, $fileName){
    $index = 1;
    while (file_exists($path."/".$fileName)) 
    {
        $baseNameEndIndex = strrpos($fileName, '_'); 
        $extensionStartIndex = strrpos($fileName, '.');
        if($baseNameEndIndex <= 0){
            $baseNameEndIndex = $extensionStartIndex;
        }
        $baseName = substr($fileName, 0, $baseNameEndIndex)."_".$index; 
        $extension = substr($fileName, $extensionStartIndex+1, strlen($fileName)-$extensionStartIndex);
        $fileName = $baseName.".".$extension;
        $index++ ;
    }
    return $fileName;
}//end nextUnusedFileName


//main

$dir = "images";
$filename = "123.jpg";

$filename = nextUnusedFileName($dir, $filename);

echo $filename;
?>