Find string pattern from end - php

Question

I am trying to find if a string is of a format <initial_part_of_name>_0.pdf i.e.
Find if it ends with .pdf (could be eliminated using rtrim)
The initial part is followed by an _ underscore.
The underscore is followed by a whole number (0, 1, 2, ... , etc.)
What could be the optimum way to achieve this? I have tried combinations of the string functions strpos (to find the position. but could not get to do anything from the end of the string).
Any pointers would be appreciated!
Edit:
Sample strings:
public://Big_Data_Tutorial_part4_0.pdf
public://Big_Data_Tutorial_part4_1.pdf
public://Big_Data_Tutorial_part4_3.pdf
The reason why I need to check is to avoid duplicate files which are stored with the _<number> appended.

Answer 1

You can use preg_match() function for matching patterns
Check the function preg_match()
preg_match("/(.*)_(\d+)\.pdf$/", "<initial_part_of_name>_0.pdf",$arr);
In $arr[1], you will get the <initial_part_of_name>
in $arr[2], you will get the number after underscore

Answer 2

a non-array and regex way
$str1 = "public://Big_Data_Tutorial_part4_0a.pdf"; // no match because 0a
$str2 = "public://Big_Data_Tutorial_part4_1.pdf"; // match
$str3 = "public://Big_Data_Tutorial_part4_3.pdf"; // match
$last_part = strrchr($str1, "_");
if (trim(strstr($last_part, ".", true), "_0..9") == "" && strstr($last_part, ".") == ".pdf") {
echo "match";
}

Answer 3

$str = '<initial_part_of_name>_0.pdf';
$exploded = explode('.', $str);
echo $exploded[1];

Answer 4

This could be done using regex. Something like
^[0-9A-Za-z]+\_[\d]\.pdf$
Implementation:
$filename = '<initial_part_of_name>_0.pdf';
if(preg_match('/^[0-9A-Za-z]+\_[\d]\.pdf$/i', $filename)){
// name pattern Matched
}
SOLUTION 2
use pathinfo()
$filename = '<initial_part_of_name>_0.pdf';
$path_parts = pathinfo($filename);
if(strtolower($path_parts['extension']) == 'pdf') {
if(preg_match('/.*_[\d]$/', $path_parts['filename'])){
// name pattern Matched
}
} else {
// Not a PDF file
}