Changing a value in an html tag using RegEx

Question

As a regex newbie, this is frustrating me - all help appreciated. I have something like this:

<img src="https://jdfsdf.dsfsdf.sdfsd/upload/sm/dsfsdf/sdfsdf/sdfdsf.jpg" style="..." id="..">

I want it to be:

<img src="https://jdfsdf.dsfsdf.sdfsd/upload/lg/dsfsdf/sdfsdf/sdfdsf.jpg" style="..." id="..">

Basically, changing the /sm/ to /lg/. I'd like to do this via RegEx in PHP, and I'm using http://www.phpliveregex.com/ to test.

I could do this simply, but with less robustness, using a simple PHP str_replace - for the sake of this question I'd like to keep the answers using RegEx.

I have tried to use a look-behind, like below:

(?<=<img src.+upload\/)sm

This obviously doesn't work, but the code below does match to the desired point.

<img src.+upload\/

I'm stumped. Any assistance or links to a decent tutorial that covers this would be greatly appreciated.

Dieterg · Accepted Answer · 2013-11-18 07:24:52Z

6

You need to capture your result into a group. Your regex will look like this:

(<img src.+upload/)(sm)([^>]+>)

As you can see you can capture groups by adding parentheses. Now it's just the matter of using these groups and replacing the values.

$string = '<img src="https://jdfsdf.dsfsdf.sdfsd/upload/sm/dsfsdf/sdfsdf/sdfdsf.jpg" style="..." id="..">';
$pattern = '/(<img src.+upload/)(sm)([^>]+>)/i';
$replacement = '$1lg$3';
echo preg_replace($pattern, $replacement, $string);

Try this regex out at http://gskinner.com/RegExr/

edited Nov 18, 2013 at 7:24

answered Nov 18, 2013 at 7:06

Dieterg

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2 Comments

JonRed Over a year ago

Is that replacement pattern supposed to be '$1lg$3'? Great answer, btw.

JonRed Over a year ago

Accepted this answer, but it does need an escape in the $pattern declaration: $pattern = '/(<img src.+upload\/)(sm)([^>]+>)/i'; Thank you.

Andrew · Accepted Answer · 2013-11-18 07:08:15Z

1

Try this:

preg_replace('@(<img[^>]+http[^\'">]+)/sm/@i', '$1/lg/', $str1);

answered Nov 18, 2013 at 7:08

Andrew

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Comments

newman · Accepted Answer · 2013-11-18 07:05:21Z

0

You can use str_replace for this. Regexp for this task is very hard.

answered Nov 18, 2013 at 7:05

newman

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