Modify my regex so that pattern search should not be case sensitive

Question

I have following php code that removes whole word that matches the pattern

$patterns = ["re", "get", "ER"];
$string = "You are definitely getting better today";
$alternations = implode('|', $patterns);
$re = '(?!(?<=\s)(?:'.$alternations.')(?=\s))\S*(?:'.$alternations.')\S*';
$string = preg_replace('#'.$re.'#', '', $string);
$string = preg_replace('#\h{2,}#', ' ', $string);
echo $string;

I want two modifications

The pattern search should not be case sensitive e.g. the pattern ER must remove better in $string
If removed word in $string have line breaks before or after it, only one line break should be removed.

If $string is

You are definitely getting
better
today

Output must be

You definitely
today

Sample PHP Code

Regards,

Possible duplicate of [Regex: ignore case sensitivity](https://stackoverflow.com/questions/9655164/regex-ignore-case-sensitivity) — Code_Ninja, Jul 23 '18 at 05:26
Possible duplicate of [Remove all line-breaks, but except only one break? ](https://stackoverflow.com/questions/35663750/remove-all-line-breaks-but-except-only-one-break) — Code_Ninja, Jul 23 '18 at 05:28
@Code_Ninja If OP means to match an optional line break at the start of the pattern, [this post](https://stackoverflow.com/questions/35663750/) does not seem helpful. — Wiktor Stribiżew, Jul 23 '18 at 06:43
@Wiktor Stribiżew your modifications work perfectly, please write it in answer. — DMP, Jul 24 '18 at 03:22

score 1 · Accepted Answer · answered Jul 24 '18 at 05:09

You may use

$patterns = ["re", "get", "ER"];
$string = "You are definitely getting\nbetter\ntoday";
$alternations = implode('|', $patterns);
$re = '\R?(?!(?<=\s)(?:'.$alternations.')(?=\s))\S*(?:'.$alternations.')\S*';
$string = preg_replace('#'.$re.'#i', '', $string);
$string = preg_replace('#\h{2,}#', ' ', $string);
echo $string;

See the PHP demo.

While the i modifier provides the case insensitivity to regex matching, another, less obvious thing here is that you need to add an optional line break pattern.

That line break can be matched in various ways, but in PHP PCRE, you may easily match it with \R construct.

Adding a ? quantifier after it, you may make it match 1 or 0 times, i.e. make it optional, so that the whole pattern could still match at the start of the string.

Modify my regex so that pattern search should not be case sensitive

1 Answers1