正则表达式排除一切，但个别地

Question

Current Regex:

([^ipd])

I get the correct output, although it doesn't deselect them individually. I'm wanting to deselect only i , p and d individually.

Want:

i
p
d

Don't want:

ipd
ip
pd
id

etc.

I've tried:

([^ipd] {1})
([^i|p|d$])

Answer 1

^[ipd]$

You need to add anchors to limit the matches to just i,p,d .

$re = "/^[ipd]$/m"; 
$str = "i\np\nd\n\nDon't Want\nipd\nip\npd\nid"; 

preg_match_all($re, $str, $matches);

Answer 2

This work in string and with separate characters:

[^ipd]|(?<=[ipd])[ipd]|[ipd](?=[ipd])

where:

• [^ipd] - not "i","p" or "d";
• (?<=[ipd])[ipd] - match "i","p" or "d" if it is proceeded by "i","p" or "d";
• [ipd](?=[ipd]) - "i","p" or "d" if it is fallowed by "i","p" or "d";

DEMO