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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.

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4 Answers 4

Reset to default
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:

Image from debuggex

Code:

$pattern = '~(?<=/)(?:([a-z]+)(?=\d+\.gif)|(\w+)(?=from_))~i';
echo preg_replace($pattern, '', $string);

Demo

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7 Comments

Thanks, but I cannot work with nice and clean arrays here - the problem is such that I need the replacement to work with all matching instances inside a long string.
@RC: It doesn't matter. It should work with a plain string as well. See demo.
Yes it does! Sorry I had seen so many solutions with an array input that failed with a long string, so I didn't test it. Thanks so much! And also for the effort in mapping out the syntax - much appreciated!
Sorry, just realised something: how do I amend your pattern so that it ONLY replaces filenames within the images/prices/ path, and ignores all other similar filenames in other paths?
@RC: Simply change the lookbehind to (?<=images/prices/).
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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);
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4 Comments

Thanks, but if I replace the line breaks with spaces, the code fails. Only the first item is replaced - the remaining two are not. I need every matching instance in a long string to be replaced. Any ideas?
Did you check my linked demo where all the images are getting replaced. You might be missing m flag.
I'm really bad with Regex! I tried running your code with the line breaks replaced with spaces and this is the result: sandbox.onlinephpfunctions.com/code/… - the last two are not replaced.
In that case your regex will be: $re = '~(images/prices/)\D*?(from_)?(\d+\..+)~';
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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)
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2 Comments

Thanks, but if I replace the line breaks with spaces, the code fails and only displays the last item. I need every matching instance in a long string to be replaced. Any ideas?
Thanks. I'm really bad with Regex syntax, so may be missing something, but I set $re = "(?<=\bimages\/prices\/).*?(?=(from_)?\d+\.gif\b)"; and ran the code but got a Unknown modifier '.' error.
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$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;
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2 Comments

Thanks, but I cannot work with nice and clean arrays here - the problem is such that I need the replacement to work with all matching instances inside a long string.
@RC You can still use, kind of, the same regex. I updated the answer.

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