Question

$subject = "SPRINT-1.csv";
$pattern = '/^[a-zA-Z]\-[0-9]\.(csv)+$/';
if(preg_match($pattern, $subject)) {
 echo "Match";
} else {
 echo "NOPE";
}

or

$subject = "SPRINT-1.csv";
$pattern = '/^\w\-\.(csv)+$/';
if(preg_match($pattern, $subject)) {
 echo "Match";
} else {
 echo "NOPE";
}

Answer 1

A character class […] does only describe one single character. So [a-zA-Z] describes one character out of a–z, A–Z. The same applies to \w (that’s also a character class).

You forgot to describe the quantity the characters from that character classes may appear, like:

• ?: zero or one repetition
• *: zero or more repetitions
• +: one or more repetitions