替换除最后一个之前的一个以外的所有_

Question

I have the following url:

http://distilleryimage3_s3_amazonaws_com/8af11cdcf11e286b022000ae90285_7_jpg

I want to replace the _ with . . However, the _7 at the end should be kept - it is not a dot.

So, basically it should look like:

http://distilleryimage3.s3.amazonaws.com/8af11cdcf11e286b022000ae90285_7.jpg

If I use str_replace it will replace all the _ but I need to keep that one there. How can I do this?

Answer 1

Use this ( corrected now! )

<?php
$subject = 'http://distilleryimage3_s3_amazonaws_com/8af11cdcf11e286b022000ae90285_7_jpg';
$pattern = '/(_)(?!\d_jpg)/';


var_dump(preg_replace($pattern, '.', $subject));

This outputs

http://distilleryimage3.s3.amazonaws.com/8af11cdcf11e286b022000ae90285_7.jpg

Answer 2

You can use this negative lookahead based regex code:

$s='http://distilleryimage3_s3_amazonaws_com/8af11cdcf11e286b022000ae90285_7_jpg';
$repl = preg_replace('/_(?![^_]*_[^_]*$)/', '.', $s);
//=> http://distilleryimage3.s3.amazonaws.com/8af11cdcf11e286b022000ae90285_7.jpg

Answer 3

Here's a solution that doesn't use regex (works for all numbers, so this won't fail if the number is different from 7 ; it doesn't have to be a number -- a string works, too):

 <?php

$haystack = 'http://distilleryimage3_s3_amazonaws_com/8af11cdcf11e286b022000ae90285_7_jpg';

//replacing all '_' with '.'
$haystack = str_replace('_', '.', $haystack);

//finding second last occurence of '.'
$n = strrpos($haystack, '.', strrpos($haystack, '.') - strlen($haystack) - 1);

//replacing the nth character to '_'
$haystack[$n] = '_';

echo $haystack;

Output:

http://distilleryimage3.s3.amazonaws.com/8af11cdcf11e286b022000ae90285_7.jpg

Demo!

Answer 4

The final _ in a string that is not itself.

 _(?=[^_]+$)

Edit: my assumption is that this question needs specific knowledge of file extensions to answered correctly.