REGEX for first two characters from a set of values? - php

Question

I have a set of starting 2 alphabets as:
$arr = ['AB', 'DC', 'LF']
Problem: I need to make a regex (in PHP and TypeSript) that passes only those strings which starts with above values.
Example:
Valid:
ABwerty45^&*jk
ABwerrtty
LF%$^erftgt5234
Invalid:
TABYR56H
ab7877
Abtyu7
Any help is appreciated.

Answer 1

You could join() the array and compose a regex with an alternation like this:
<?php
$strings = <<<DATA
ABwerty45^&*jk
ABwerrtty
LF%$^erftgt5234
TABYR56H
ab7877
Abtyu7
DATA;
$arr = ['AB', 'DC', 'LF'];
$regex = '~^(?:' . join('|', $arr) . ').*~m';
if (preg_match_all($regex, $strings, $matches)) {
print_r($matches);
}
?>
Which yields
Array
(
[0] => Array
(
[0] => ABwerty45^&*jk
[1] => ABwerrtty
[2] => LF%$^erftgt5234
)
)
Basically, this says:
^ # match the start of the string
(?:AB|DC|LF) # AB or DC or LF
.* # 0+ characters in that line

Answer 2

Instead of a regex you could check if the first 2 characters are present in the array:
$arr = ['AB', 'DC', 'LF'];
if (in_array(substr("ABwerty45^&*jk",0, 2), $arr)) {
// ...
}
Demo
const strings = [
"ABwerty45^&*jk",
"ABwerrtty",
"LF%$^erftgt5234",
"TABYR56H",
"ab7877",
"Abtyu7"
];
const arr = ['AB', 'DC', 'LF'];
strings.forEach((s) => {
let match = arr.includes(s.substring(0, 2));
match ? console.log("Match : ", s) : console.log("No match: ", s);
});