how can I check for the firs three letters of the word with php?

Follow up (for interest)
substr_compare runs almost in linear time - the length of the string and substring have little impact on running time
the other method increases the longer the strings get.

Consider this sample

<?php
$test = "934373648487548378374238943248726348268234";
$sub = "9343736484875483783742389432487263482682";
$len = strlen($sub);
$start = microtime(true);
for($i = 0; $i < 100000;$i++) {
  if (substr($test, 0, $len) == $sub) {
    $result = true;
  }
  else {
    $result = false;
  }
}
$end = microtime(true);
$one = $end - $start;
$start = microtime(true);
for($i = 0; $i < 100000;$i++) {
  $result = substr_compare($test, $sub, 0, $len);
}
$end = microtime(true);
$two = $end - $start;
echo "One: {$one}<br/>";
echo "Two: {$two}<br/>";

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Results for the above

One: 0.15969896316528
Two: 0.019267082214355

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With
$sub="934"

One: 0.029422044754028
Two: 0.018805027008057

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thank you all

@Braveheartli,

Is there any particular reason you did not choose the first post as the correct answer - it is the same as the accepted post but was there first - by acknowledgement of the second poster?

Dear Julian Hansen,
I'm pretty sure that your answer was correct
I tried yours answer first, but somehow i couldn't get the result...most  probably my fault

@Braverhertli,

I was not referring to my answer I was referring to Rgonzo1971.

if (substr($customerid ,0,3) == "934") echo "yes";

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This was posted first and is the same as the accepted answer.