Question

match a // in a line of array and replace // with blank space if its not inside " ".
For example I have this line:

//this is a test
"this is a // test"

the output should be:

"this is a // test"

it will ignore // inside ""

for now I’ve come up with this regex:

$string[$i] = preg_replace('#(?<!")//.*(?!")#',' ',$string[$i]);

but this does’t work if the // is in the middle or last part of a line.

Answer 1

Since you don’t have to worry about quotes that span multiple lines, this makes your job significantly easier.

One approach would be to go through the input line-by-line and explode() each line using " as the delimiter:

$processed = '';

/* Split the input into an array with one (non-empty) line per element.
 *
 * Note that this also allows us to consolidate and normalize line endings
 *  in $processed.
 */
foreach( preg_split("/[\r\n]+/", $input) as $line )
{
  $split = explode('"', $line);

  /* Even-numbered indices inside $split are outside quotes. */
  $count = count($split);
  for( $i = 0; $i < $count; $i += 2 )
  {
    $pos = strpos($split[$i], '//');
    if( $pos !== false )
    {
      /* We have detected '//' outside of quotes.  Discard the rest of the line. */
      if( $i > 0 )
      {
        /* If $i > 0, then we have some quoted text to put back. */
        $processed .= implode('"', array_slice($split, 0, $i)) . '"';
      }

      /* Add all the text in the current token up until the '//'. */
      $processed .= substr($split[$i], 0, $pos);

      /* Go to the next line. */
      $processed .= PHP_EOL;
      continue 2;
    }
  }

  /* If we get to this point, we detected no '//' sequences outside of quotes. */
  $processed .= $line . PHP_EOL;
}
echo $processed;

Using the following test string:

<?php
$input = <<<END
//this is a test
"this is a // test"
"Find me some horsemen!" // said the king, or "king // jester" as I like to call him.
"I am walking toward a bright light." "This is a // test" // "Who are you?"
END;

We get the following output:

"this is a // test"
"Find me some horsemen!" 
"I am walking toward a bright light." "This is a // test"