Returning multiple values in PHP checking if they exist and are set

EDIT

Old code probably didn't work as expected. Prepended ./ to images to find the right files. Now also using character ranges for case-insensitive file-extension search.

Why not glob? It looks for files based on a pattern you pass it and return an array with matched files.

$files = glob ('./images/' . $field . '*.[jJ][pP][gG]');

if (is_array($files) && count($files)) {
   // if you need to remove the `./` from the front of the file name,
   // use the following line
   $files = array_map(function($val) { return substr($val, 2); }, $files);
   return implode(',', $files);
}

It can search directories using a wildcard. See the first comment on documentation page for an explanation of how it works. Basically, * is a wildcard meaning match any character.

It can all be done quite simply with a couple of loops like this

$field = '123456';

$max_loop = 10;
$files_to_check = [];
$result = '';

// generate filenames with _number added
// first the odd filename with no additional numeric
$files_to_check[] = "images/$field.jpg";
// loop all the others
for ( $x=1; $x <= max_loop; $x++) {
    $files_to_check[] = sprintf('images/%s_%d.jpg', $field, $x); 
}

foreach ( $files_to_check as $file ) {
    if (file_exists($file) ) {
        $result = $file . ',';
    }
}
$result = trim($result, ',');

return $result;

SPL (StandardPHPLibrary) can also do the job. I read the directory first, then check for it's existence by isFile() method (also if it's a file) and finally store the matching filename to array.

$iterator = new DirectoryIterator(__DIR__);
foreach ($iterator as $fileinfo) {
    $isFile = $fileinfo->isFile();
    $isMatch = stripos($fileinfo->getFilename(), $field) !== false;
    if ($isFile && $isMatch) {
        $myFile[] = $fileinfo->getFilename()
    }
}

echo implode(",", $myFile);

Read more: DirectoryIterator PHP manual page

Try something like this. First in here you create a list of possible file endings (here up from _0.jpgup to_100.jpg). The first one is the original without_X.jpg`.

Then you loop over all and collect the existing files and finally implode them to get a comma sperated list.

$extensions = [".jpg",];
for ($i = 0; $i <= 100; $i++){
    $extensions[] = sprintf("_%d.jpg", $i);
}
$existing_files = [];
foreach ($extensions as $extension) {
    $filename = "images/" . $file . $extension;
    if(file_exists($filename)){
        $existing_files[] = $filename;
    }
}

$result = implode(",", $existing_files);

If you are not calling function ,return is no need ! Assign one variable is better

$format = array(".JPG","_1.JPG","_2.JPG");
$file = array();
foreach ($format as $value) {
  if (file_exists('images/' . $field.$value)) {
  $file[] = 'images/'. $field.$value;
  }
}

$result = "";
$last = count($file)-1; //last index key
foreach ($file as $k=>$f) {
  if(isset($f)){
    ($last == $k) ? $result.= $f : $result.= $f.",";
  }
}
var_dump($result);