regex not working as expected when matching file names with wildcards - php

Question

I am writing a PHP function that takes an array of file names and removes file names from the array if they do not match a set of criteria input by the user. The function iterates through the array and compares each value to a regex. The regex is formed by inserting variables from user input. If the user didn't specify a variable, regex wildcard characters are inserted in the variable's place. The file names are all very systematic, like 2020-06-N-1.txt so I know exactly how many characters to expect in the file names and from the user input. However, when I run the code, file names that don't match the regex are still in the array. Some non-matching file names are taken out, but many others are left in. Parts of my PHP code are below. Any help is appreciated.
function fileFilter() {
global $fileArray, $fileFilterPattern;
/* The loop starts at 2 and goes to count()-1 because the first 2 elements were removed
earlier with unset */
for ($j = 2; $j < count($fileArray) - 1; $j++) {
if(!(preg_match($fileFilterPattern, $fileArray[$j]))) {
unset($fileArray[$j]);
}
}
return;
}
// If user does not provide a filter value, it gets converted into wildcard symbol
if ($month == '') {
$month = '..';
}
if ($year == '') {
$year = '....';
}
if ($section == '') {
$section = '.';
}
$fileFilterPattern = "/{$year}-{$month}-{$section}-.\.txt/";
/* function only runs if user applied at least one filter */
if (!($month == '..' && $year == '....' && $section == '.')) {
fileFilter();
}
Below I have included an example of how the array contains elements that aren't matches. I obtain my output array using echo json_encode($fileArray);
My input:
month is ""
year is ""
section is "L"
Expected result:
Array contains only files that have L in the section spot (YEAR-MONTH-**SECTION**-NUMBER.txt)
Resulting array:
{"8":"2020-06-L-1.txt","9":"2020-06-L-2.txt","10":"2020-06-L-3.txt","11":"2020-06-L-4.txt","12":"2020-06-L-5.txt","15":"2020-06-N-3.txt","16":"2020-06-N-4.txt","17":"2020-06-N-5.txt","18":"2020-06-N-6.txt","19":"2020-06-O-1.txt","20":"2020-06-O-2.txt","21":"2020-06-O-3.txt","22":"2020-06-O-4.txt","23":"2020-06-S-1.txt","24":"2020-06-S-2.txt","25":"2020-06-S-3.txt"}

Answer 1

The problem is using unset() inside a loop. On the next iteration, the index is no longer the same as it was before you messed with the array using unset(). Sometimes, you deal with this by using array_values(), but in this case it's simpler to just build a second array that has only the values you want. The following code works. I've used array_values() just to take the string that you provided and get the indexes back to normal.
That said, since the "first 2 elements were removed
earlier with unset" you need to run array_values() on the array before you get to this part.
<?php
$str ='{"8":"2020-06-L-1.txt","9":"2020-06-L-2.txt","10":"2020-06-L-3.txt","11":"2020-06-L-4.txt","12":"2020-06-L-5.txt","15":"2020-06-N-3.txt","16":"2020-06-N-4.txt","17":"2020-06-N-5.txt","18":"2020-06-N-6.txt","19":"2020-06-O-1.txt","20":"2020-06-O-2.txt","21":"2020-06-O-3.txt","22":"2020-06-O-4.txt","23":"2020-06-S-1.txt","24":"2020-06-S-2.txt","25":"2020-06-S-3.txt"}';
$fileArray = json_decode($str, true);
$fileArray = array_values($fileArray);
echo '<p>fileArray: ';
var_dump($fileArray);
echo '</p>';
function fileFilter() {
global $fileArray, $fileFilterPattern;
$filteredArray = [];
for ($j = 0; $j < count($fileArray); $j++) {
if(preg_match($fileFilterPattern, $fileArray[$j]) === 1) {
//unset($fileArray[$j]);
array_push($filteredArray, $fileArray[$j]);
}
}
echo '<p>filteredArray: ';
var_dump($filteredArray);
echo '</p>';
//return;
}
$month =='';
$year = '';
// If user does not provide a filter value, it gets converted into wildcard symbol
if ($month == '') {
$month = '..';
}
if ($year == '') {
$year = '....';
}
if ($section == '') {
$section = '.';
}
$section = 'L';
$fileFilterPattern = "#{$year}-{$month}-{$section}-.\.txt#";
echo '<p>fileFilterPattern: ';
var_dump($fileFilterPattern);
echo '</p>';
/* function only runs if user applied at least one filter */
if (!($month == '..' && $year == '....' && $section == '.')) {
fileFilter();
}
?>

Answer 2

The main problem is that the count decreases each time you unset, so you should define the count once. Assuming the -1 and $j = 2 are correct for your scenario:
$count = count($fileArray) - 1;
for ($j = 2; $j < $count; $j++) {
if(!(preg_match($fileFilterPattern, $fileArray[$j]))) {
unset($fileArray[$j]);
}
}
There are others ways where you don't have to assume and then keep track of the keys:
foreach($fileArray as $k => $v) {
if(!preg_match($fileFilterPattern, $v)) {
unset($fileArray[$k]);
}
}
I would get rid of your fileFilter function and use this handy function instead, which will return all items that match the pattern:
$fileArray = preg_grep($fileFilterPattern, $fileArray);