Regex in PHP: Replacing text between strings - php

Question

Okay I have made some progress on a problem I am solving, but need some help with a small glitch.
I need to remove all characters from the filenames in the specific path images/prices/ BEFORE the first digit, except for where there is from_, in which case remove all characters from the filename BEFORE from_.
Examples:
BEFORE AFTER
images/prices/abcde40.gif > images/prices/40.gif
images/prices/UgfVe5559.gif > images/prices/5559.gif
images/prices/wedsxcdfrom_88457.gif > images/prices/from_88457.gif
What I've done:
$pattern = '%images/(.+?)/([^0-9]+?)(from_|)([0-9]+?)\.gif%';
$replace = 'images/\\1/\\3\\4.gif';
$string = "AAA images/prices/abcde40.gif BBB images/prices/wedsxcdfrom_88457.gif CCC images/prices/UgfVe5559.gif DDD";
$newstring = str_ireplace('from_','733694521548',$string);
while(preg_match($pattern,$newstring)){
$newstring=preg_replace($pattern,$replace,$newstring);
}
$newstring=str_ireplace('733694521548','from_',$newstring);
echo "Original:\n$string\n\nNew:\n$newstring";
My expected output is:
AAA images/prices/40.gif BBB images/prices/from_88457.gif CCC images/prices/5559.gif DDD"
But instead I am getting:
AAA images/prices/40.gif BBB images/from_88457.gif CCC images/5559.gif DDD
The prices/ part of the path is missing from the last two paths.
Note that the AAA, BBB etc. portions are just placeholders. In reality the paths are scattered all across a raw HTML file parsed into a string, so we cannot rely on any pattern in between occurrences of the text to be replaced.
Also, I know the method I am using of substituting from_ is hacky, but this is purely for a local file operation and not for a production server, so I am okay with it. However if there is a better way, I am all ears!
Thanks for any assistance.

Answer 1

You can use lookaround assertions:
preg_replace('~(?<=/)(?:([a-z]+)(?=\d+\.gif)|(\w+)(?=from_))~i', '', $value);
Explanation:
(?<=/) # If preceded by a '/':
(?: # Begin group
([a-z]+) # Match alphabets from a-z, one or more times
(?=\d+\.gif) # If followed followed by digit(s) and '.gif'
| # OR
(\w+) # Match word characters, one or more times
(?=from_) # If followed by 'from_'
) # End group
Visualization:
Code:
$pattern = '~(?<=/)(?:([a-z]+)(?=\d+\.gif)|(\w+)(?=from_))~i';
echo preg_replace($pattern, '', $string);
Demo

Answer 2

You can use this regex for replacement:
^(images/prices/)\D*?(from_)?(\d+\..+)$
And use this expression for replacement:
$1$2$3
RegEx Demo
Code:
$re = '~^(images/prices/)\D*?(from_)?(\d+\..+)$~m';
$str = "images/prices/abcde40.gif\nimages/prices/UgfVe5559.gif\nimages/prices/wedsxcdfrom_88457.gif";
$result = preg_replace($re, '$1$2$3', $str);

Answer 3

You can try with Lookaround as well. Just replace with blank string.
(?<=^images\/prices\/).*?(?=(from_)?\d+\.gif$)
regex101 demo
Sample code: (directly from above site)
$re = "/(?<=^images\\/prices\\/).*?(?=(from_)?\\d+\\.gif$)/m";
$str = "images/prices/abcde40.gif\nimages/prices/UgfVe5559.gif\nimages/prices/wedsxcdfrom_88457.gif";
$subst = '';
$result = preg_replace($re, $subst, $str);
If string is not multi-line then use \b as word boundary instead of ^ and $ to match start and end of the line/string.
(?<=\bimages\/prices\/).*?(?=(from_)?\d+\.gif\b)

Answer 4

$arr = array(
'images/prices/abcde40.gif',
'images/prices/UgfVe5559.gif',
'images/prices/wedsxcdfrom_88457.gif'
);
foreach($arr as $str){
echo preg_replace('#images/prices/.*?((from_|\d).*)#i','images/prices/$1',$str);
}
DEMO
EDIT:
$str = 'AAA images/prices/abcde40.gif BBB images/prices/wedsxcdfrom_88457.gif CCC images/prices/UgfVe5559.gif DDD';
echo preg_replace('#images/prices/.*?((from_|\d).*?\s|$)#i','images/prices/$1',$str), PHP_EOL;