match the first & last whole word in a variable - php

Question

I use php preg_match to match the first & last word in a variable with a given first & last specific words,
example:
$first_word = 't'; // I want to force 'this'
$last_word = 'ne'; // I want to force 'done'
$str = 'this function can be done';
if(preg_match('/^' . $first_word . '(.*)' . $last_word .'$/' , $str))
{
echo 'true';
}
But the problem is i want to force match the whole word at (starting & ending) not the first or last characters.

Answer 1

Using \b as boudary word limit in search:
$first_word = 't'; // I want to force 'this'
$last_word = 'ne'; // I want to force 'done'
$str = 'this function can be done';
if(preg_match('/^' . $first_word . '\b(.*)\b' . $last_word .'$/' , $str))
{
echo 'true';
}

Answer 2

I would go about this in a slightly different way:
$firstword = 't';
$lastword = 'ne';
$string = 'this function can be done';
$words = explode(' ', $string);
if (preg_match("/^{$firstword}/i", reset($words)) && preg_match("/{$lastword}$/i", end($words)))
{
echo 'true';
}
==========================================
Here's another way to achieve the same thing
$firstword = 'this';
$lastword = 'done';
$string = 'this can be done';
$words = explode(' ', $string);
if (reset($words) === $firstword && end($words) === $lastword)
{
echo 'true';
}
This is always going to echo true, because we know the firstword and lastword are correct, try changing them to something else and it will not echo true.

Answer 3

I wrote a function to get Start of sentence but it is not any regex in it.
You can write for end like this. I don't add function for the end because of its long...
<?php
function StartSearch($start, $sentence)
{
$data = explode(" ", $sentence);
$flag = false;
$ret = array();
foreach ($data as $val)
{
for($i = 0, $j = 0;$i < strlen($val), $j < strlen($start);$i++)
{
if ($i == 0 && $val{$i} != $start{$j})
break;
if ($flag && $val{$i} != $start{$j})
break;
if ($val{$i} == $start{$j})
{
$flag = true;
$j++;
}
}
if ($j == strlen($start))
{
$ret[] = $val;
}
}
return $ret;
}
print_r(StartSearch("th", $str));
?>