prefix_email_subject.php

#!/bin/php
<?php
$SUBJECT_PREFIX = "Subject: ";

$allHeadersRead = FALSE;
$subject = NULL;


while($f = fgets(STDIN)){
  $allHeadersRead |= (trim($f) === '');
  if ($subject != NULL) {
    if (preg_match("#^\\s#", $f)) {
      $subject .= iconv_mime_decode(substr($f, 1), 2, "UTF-8");
    } else {
      $prefix = '['.$argv[1].']';
      echo iconv_mime_encode(
          'Subject',
          (strpos($subject, $prefix) === FALSE ? "$prefix " : '').$subject,
          array(
            'scheme' => 'Q',
            'input-charset' => 'UTF-8',
            'output-charset' => 'UTF-8'
          )
        )."\r\n";
      $subject = NULL;
      echo $f;
    }
  } else if ($argc > 1 && !$allHeadersRead && substr($f, 0, strlen($SUBJECT_PREFIX)) === $SUBJECT_PREFIX) {
    $subject = iconv_mime_decode(substr($f, strlen($SUBJECT_PREFIX)), 2, "UTF-8");
    $allHeadersRead = TRUE;
  } else {
    echo $f;
  }
}