What is the difference between [abc] and /^[abc]+$/ in terms of regex patterns in PHP?

The difference between [abc] and /^[abc]+$/ in regex patterns in PHP is that [abc] matches any single character that is either 'a', 'b', or 'c', while /^[abc]+$/ matches a sequence of one or more characters that are 'a', 'b', or 'c' from the beginning to the end of the string. The former checks for individual characters, while the latter checks for a whole sequence of characters. 

// Using [abc] to match any single character 'a', 'b', or 'c'
$string = "abc";
if (preg_match("/[abc]/", $string)) {
    echo "Match found using [abc]";
}

// Using /^[abc]+$/ to match a sequence of one or more characters 'a', 'b', or 'c'
$string = "abccba";
if (preg_match("/^[abc]+$/", $string)) {
    echo "Match found using /^[abc]+$/";
}

Keywords

PHP regex patterns regular expressions syntax matching.

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