$re = '/if\s*(\((?>[^()]|(?1))*\))(*SKIP)(*F)|(\w+)(\s*<=[^;]*)/s';
$str = 'always @(posedge clk or negedge rst_n)
if(!rst_n)begin
d1 <= 0; //perl_comment_4
//perl_comment_5
d2 <= 1 //perl_comment_6
+ 2;
end
else if( d3 <= d4 && ( d5 <= 3 ) ) begin
d6 <= d7 +
(d8 <= d9 ? 1 : 0);
//perl_comment_7
d10 <= d11 <=
d12
+ d13
<= d14 ? 1 : 0;
end';
$subst = "$2_yes$3";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php