php-interact.php: evaluate single-line php expressions.
Exit by calling `exit` or by typing the EOF character (^D on *nix, ^C on Windows).

<?php

// TODO: trim error message *before* elucidating newlines...
//  (else the introduced-char+newline doesn't get trimmed away)

/***  
  Here is a bare-bones version of what this script does:

    $fp = fopen("php://stdin", "r");
    while(!feof($fp)) {
      echo "\nphp> ";
      eval(fgets($fp));
      }
    fclose($fp); 

  It is fleshed out to treat I/O and error-messages a bit better.
***/


error_reporting(E_ALL|E_STRICT);

$fileNamePattern = preg_quote(__FILE__,'/');
$errorSuffixPattern = preg_quote(": eval()'d code on line 1");
define("ERROR_MESG_PATTERN", "/" . " in $fileNamePattern\([[:digit:]]+\) $errorSuffixPattern" . "/" );

//echo "the error-message pattern is: $errorMesgPattern";

function myCleanUp($output) {
  $obviousNewline ="⏎\n";   // Unicode "Return Symbol" (U+23CE)
  $output = preg_replace("/\n/",$obviousNewline,$output);
  if (($output !== '') && substr($output,-1) !== "\n") { $output .= "\n"; }
  // Or, just always append \n?
  $outputShortenErrorMsg = preg_replace(ERROR_MESG_PATTERN,'',$output);
  return (($outputShortenErrorMsg === $output) ? $output : ('>>> '.ltrim($outputShortenErrorMsg)));

  // Approximations (e.g. bugs):
  // We assume that if __FILE__ and following error-like text appears anywhere in the output,  
  // then it indicates an error actually occurred, and that
  // error-message has some extraneous whitespace at the very start of the output.
  // [We trim that and add ">>>"; if there were multiple errors or they weren't at the start,
  //  we just muddled things.]
  //    echo "hi",$undefdVar,"bye";
  //
  // Future approach: add a try-catch around the code we eval?  
  //   (What about 'notice' which is already caught/handled?)
  }


$fp = fopen("php://stdin", "r");
while(!feof($fp)) {
    echo "php> ";
    $oneLineIn = fgets($fp);
    ob_start();
    eval(trim($oneLineIn));
    echo myCleanUp(ob_get_clean());
    }
fclose($fp); 

/*
 Future work: Add namespace, and try-catch, around the code we eval?
 (I tried adding a separate namespace for the eval'd code, and this
 script itself, but the 'eval'd code could still grab variables
 from the script?!  Sigh.)
*/
?>