I'm using regex to replace image source urls in an html file.
I want for example to replace img/ with <?= $folder ?>/img/
The issue:
When I run the regex multiple times it will replace img/ again, creating:
<?= $folder ?>/<?= $folder ?>/img
..and so on. Is there a way to tell regex to replace img/ if not already <?= $folder ?>/img ?
I am trying /^(?:(?!<?= $folder ?>/img).)*$/ but not sure how to first match and check if that it doesn't already contain <?= $folder ?>/img
If you prefer regex, please try:
function matchIfNot(str) {
var newstr = str.replace(/^(?!(<\?=\s\$folder\s\?>\/))(img\/)/g, "<?= $folder ?>/img/")
alert("Old string: " + str + "\nNew string: " + newstr)
}
matchIfNot("<?= $folder ?>/img/")
matchIfNot("img/")Output:
Old string: <?= $folder ?>/img/
New string: <?= $folder ?>/img/
Old string: img/
New string: <?= $folder ?>/img/
Try /(?!<\?= $folder \?>)img\//.
The bit at the beginning there, the (?!< ... ) is the notation for negative look-behind, that is, for checking if ... is earlier in the string. In this case, we're checking if the string
<\?= $folder \?> (note the escaped question marks) is earlier in the string.
If that section is found earlier in a line with img/, it will be rejected, and won't match. So, each case of img/ will only be matched once.
This regex will fail for lines with more than one occurence of img/. There might be a way to allow for multiple occurences, but it would likely be a very long regex; and in my opinion, usually when a regex gets too long, it might be time to switch to a different tool.
[PLACEHOLDER], then do your replace, then replace[PLACEHOLDER]with your full string again. I believe you can do your replace with just a single RegEx, but this way would be an alternative that's a little more linear./^(?:(?!<?= $folder ?>\/img).)*$/works fine and doesn't replace if same string is already there in input