diff --git a/web/democode/demo.html b/web/democode/demo.html
index 63bc81e..83a3fea 100644
--- a/web/democode/demo.html
+++ b/web/democode/demo.html
@@ -4,14 +4,58 @@
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 <title>WebPerl Code Demo</title>
 
-<iframe name="perlrunner" sandbox="allow-scripts"
-	src="perlrunner.html" style="display: none;"></iframe>
+<!-- ##### WebPerl - http://webperl.zero-g.net #####
+
+Copyright (c) 2018 Hauke Daempfling (haukex@zero-g.net)
+at the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB),
+Berlin, Germany, http://www.igb-berlin.de
+
+This program is free software; you can redistribute it and/or modify
+it under the same terms as Perl 5 itself: either the GNU General Public
+License as published by the Free Software Foundation (either version 1,
+or, at your option, any later version), or the "Artistic License" which
+comes with Perl 5.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+See the licenses for details.
 
-<iframe sandbox="allow-scripts" src="perleditor.html#i1f=Foo%0ABar%0AQuz&i1n=in1.txt&script=use warnings;%0Ause strict;%0A%0Awhile (<>) {%0A    s/[aeiou]/_/gi;%0A}&cmdline=perl script.pl in1.txt"
-	style="border:1px solid black;width:100%;height:20em;"></iframe>
+You should have received a copy of the licenses along with this program.
+If not, see http://perldoc.perl.org/index-licence.html
+##### -->
+
+<!-- TODO: Document
+	Notes:
+	- "perl -CSD" is recommended because files are currently always UTF-8
+	- STDIN is currently not supported, workaround is to supply files on command line
+-->
+
+<iframe name="perlrunner" sandbox="allow-scripts"
+	src="perlrunner.html" style="display:none;"></iframe>
 
-<iframe sandbox="allow-scripts" src="perleditor.html"
-	style="border:1px solid black;width:100%;height:20em;"></iframe>
+<iframe id="perl1" sandbox="allow-scripts"
+	style="border:1px solid black;width:100%;height:8em;"></iframe>
+<iframe id="perl2" sandbox="allow-scripts"
+	style="border:1px solid black;width:100%;height:40em;"></iframe>
+<script>
+document.getElementById('perl1').src =
+	"perleditor.html#" + encodeURIComponent(JSON.stringify( {
+		cmdline: "perl -e 'print \"Hello, World!\"'",
+	} ));
+document.getElementById('perl2').src =
+	"perleditor.html#" + encodeURIComponent(JSON.stringify( {
+		cmdline: "perl devoweler.pl mytext.txt other.txt",
+		script: "use warnings;\nuse strict;\n\nopen my $vfh, '>', 'vowels.txt' or die $!;\n"
+			+"while (<>) {\n\tprint $vfh $1 while s/([aeiou])/_/i;\n\tprint;\n}\nclose $vfh;",
+		script_fn: "devoweler.pl",
+		inputs: [
+			{ fn: "mytext.txt", text: "Foo\nBar\nQuz\n" },
+			{ fn: "other.txt", text: "Hello, World!" },
+		],
+		outputs : [ "vowels.txt" ],
+	} ));
+</script>
 
 </head>
 <body>
diff --git a/web/democode/perleditor.css b/web/democode/perleditor.css
new file mode 100644
index 0000000..97ea52a
--- /dev/null
+++ b/web/democode/perleditor.css
@@ -0,0 +1,33 @@
+
+body {
+	margin: 0.4em;
+}
+.text {
+	font-family: Calibri, Ubuntu, "Droid Sans", Tahoma, Arial, Helvetica, sans-serif;
+}
+pre,textarea,code,.code,.filename,.CodeMirror {
+	font-family: Consolas, "Ubuntu Mono", "Droid Sans Mono", "Lucida Console", "Courier New", Courier, monospace;
+}
+pre {
+	margin: 0;
+}
+
+.CodeMirror {
+	border: 1px solid lightgrey;
+	height: auto;
+}
+.CodeMirror-scroll {
+	max-height: 12em;
+}
+
+#runnerstate {
+	margin-top: 0.1em;
+	margin-bottom: 0.3em;
+	font-size: 0.8em;
+}
+#runnererrors {
+	background-color: rgba(255,200,200,255);
+	margin-top: 0.3em;
+	margin-bottom: 0.3em;
+	padding: 0.1em 0.2em;
+}
diff --git a/web/democode/perleditor.html b/web/democode/perleditor.html
index a90bfae..4bd48be 100644
--- a/web/democode/perleditor.html
+++ b/web/democode/perleditor.html
@@ -23,31 +23,11 @@ See the licenses for details.
 
 You should have received a copy of the licenses along with this program.
 If not, see http://perldoc.perl.org/index-licence.html
--->
+##### -->
 
 <!--cacheable--><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/normalize/8.0.0/normalize.min.css" integrity="sha256-oSrCnRYXvHG31SBifqP2PM1uje7SJUyX0nTwO2RJV54=" crossorigin="anonymous" />
 <!--cacheable--><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.39.2/codemirror.min.css" integrity="sha256-I8NyGs4wjbMuBSUE40o55W6k6P7tu/7G28/JGUUYCIs=" crossorigin="anonymous" />
-<style>
-body {
-	margin: 0.4em;
-}
-.text {
-	font-family: Calibri, Ubuntu, "Droid Sans", Tahoma, Arial, Helvetica, sans-serif;
-}
-pre,textarea,code,.code,.filename,.CodeMirror {
-	font-family: Consolas, "Ubuntu Mono", "Droid Sans Mono", "Lucida Console", "Courier New", Courier, monospace;
-}
-pre {
-	margin: 0;
-}
-.CodeMirror {
-	border: 1px solid grey;
-	height: auto;
-}
-.CodeMirror-scroll {
-	max-height: 10em;
-}
-</style>
+<link rel="stylesheet" href="perleditor.css" />
 
 <!--cacheable--><script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.39.2/codemirror.min.js" integrity="sha256-uRIJ6Wfou5cTtmcCvQNA9lvsYl8sUbZXxnfG+P79ssY=" crossorigin="anonymous"></script>
 <!--cacheable--><script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.39.2/mode/perl/perl.min.js" integrity="sha256-Uu9QBfi8gU6J/MzQunal8ewmY+i/BbCkBrcAXA5bcCM=" crossorigin="anonymous"></script>
@@ -55,6 +35,11 @@ pre {
 <script>
 "use strict";
 
+var mergeStdOutErr = 0; //TODO Later: make an options hash instead of individual variable(s)?
+var perlRunner; // the Perl runner iframe found by findPerlRunner()
+var buttonBlockers = {}; // for updateButtonState()
+var lastExitStatus; // for runnerState()
+
 function makeCM (textarea,plain,ro) {
 	return CodeMirror.fromTextArea( textarea[0], {
 		viewportMargin: Infinity, // so browser's search works, not good for long documents though
@@ -65,67 +50,94 @@ function makeCM (textarea,plain,ro) {
 	} );
 }
 
-var mergeStdOutErr = 0;
+function runnerState (text) {
+	$('#runnerstate').text( text
+		+ (lastExitStatus ? ' (last exit status was '+lastExitStatus+')'
+			: '') );
+}
+
+function updateButtonState () {
+	$('#runperl').prop("disabled",
+		Object.keys(buttonBlockers).length>0 );
+}
 
-var cm_std = { 1:null, 2:null };   // 1=stdout, 2=stderr
-function stdOutput (which, data) { // 1=stdout, 2=stderr
+function stdOutput (which, data) { // which: 1=stdout, 2=stderr
 	if (mergeStdOutErr) which = 1;
-	if (!cm_std[which]) {
-		var div = $(which==1?'#stdout':'#stderr');
-		div.show();
-		cm_std[which] = makeCM($('textarea',div),1,1);
-		div.data('CodeMirrorInstance', cm_std[which]);
+	var div = $(which==1?'#stdout':'#stderr');
+	div.show();
+	var cm = div.data('CodeMirrorInstance');
+	if (!cm) {
+		cm = makeCM($('textarea',div),1,1);
+		div.data('CodeMirrorInstance', cm);
 	}
 	if (data && data.length)
-		cm_std[which].setValue( cm_std[which].getValue() + data );
+		cm.setValue( cm.getValue() + data );
 }
 function clearStdOutput () {
-	if (cm_std["1"]) cm_std["1"].setValue("");
-	if (cm_std["2"]) cm_std["2"].setValue("");
+	$('#stdout,#stderr').each(function (i) {
+		var div = $(this);
+		var cm = div.data('CodeMirrorInstance');
+		if (cm) cm.setValue('');
+		div.hide();
+	});
 }
 
-var perlRunner;
+function findPerlRunner () {
+	// assume calling this function means the runner isn't available
+	buttonBlockers.runnerState = 1;
+	updateButtonState();
+	// poll for perlRunner, which gets set by the message listener
+	var pollUntil = Date.now() + 10*1000; // milliseconds
+	var pollId;
+	pollId = window.setInterval( function () {
+		if (perlRunner)
+			window.clearInterval(pollId);
+		else if ( Date.now()>pollUntil ) {
+			if (window.confirm("Perl does not appear to have loaded yet, keep waiting?\n"
+			    +"(If you are on a slow connection, click OK to keep waiting.)"))
+				pollUntil = Date.now() + 10*1000;
+			else
+				window.clearInterval(pollId);
+		}
+		else
+			if (window.parent && window.parent.frames["perlrunner"])
+				window.parent.frames["perlrunner"].postMessage(
+					{perlRunnerDiscovery:1}, '*');
+	}, 100);
+}
 
 window.addEventListener('message', function (event) {
 	var data = event.data;
-	//console.log("editor got message", data); //DB
 	if (data["perlRunnerState"]) {
-		var disableBtn = true;
 		if ( data.perlRunnerState=="Ready" ) {
 			perlRunner = event.source;
-			disableBtn = false;
+			delete buttonBlockers.runnerState;
+			updateButtonState();
 		}
 		else if ( data.perlRunnerState=="Ended" ) {
+			if ('exitStatus' in data)
+				lastExitStatus =  ''+data.exitStatus;
+			// we know the runner will reload itself now
 			perlRunner = null;
 			findPerlRunner();
 		}
-		$('#runperl').prop("disabled",disableBtn);
+		runnerState("Perl is "+data.perlRunnerState);
 	}
-	else if (data["perlOutput"]) {
+	else if (data["perlOutput"])
 		stdOutput(data.perlOutput.chan, data.perlOutput.data);
+	else if (data["perlOutputFiles"]) {
+		data.perlOutputFiles.forEach(function (outp) {
+			setupOutputFile(outp.fn, outp.text);
+		});
+	}
+	else if (data["perlRunnerError"]) {
+		$('#runnererrors').show();
+		$('#runnererrors>pre').append(data.perlRunnerError+"\n");
 	}
 	else console.warn("Perl Editor ignoring unknown message:",data);
 });
 
-function findPerlRunner () {
-	var pollId;
-	var pollUntil = Date.now() + 10*1000; // milliseconds
-	pollId = window.setInterval( function () {
-		if (perlRunner) {
-			window.clearInterval(pollId);
-		}
-		else if ( Date.now()>pollUntil ) {
-			window.clearInterval(pollId);
-			console.error("Perl Editor could not contact Perl Runner"); //TODO: report error to user via UI (same for other console.error calls in this script)
-		}
-		else
-			if (window.parent && window.parent.frames["perlrunner"])
-				window.parent.frames["perlrunner"].postMessage(
-					{perlRunnerRegisterClient:1}, '*');
-	}, 100);
-}
-
-function parseCmdLine(str) {
+function parseCmdLine(str) { //TODO: there's a better way to do this
 	var re = /"((?:\\"|\\\\|[^"])*)"|'((?:\\'|\\\\|[^'])*)'|(\S+)/g;
 	var argv = [];
 	var match;
@@ -137,57 +149,83 @@ function parseCmdLine(str) {
 	return argv;
 }
 
-function parseParams(str) { // Thanks to https://stackoverflow.com/a/26849194
-	if (!str || !str.length) return {};
-	return str.split('&').reduce(function (params, param) {
-		var paramSplit = param.split('=').map(function (value) {
-			return decodeURIComponent(value.replace(/\+/g, ' '));
+function fetchUrl(url,cm) { // fetch the contents of a URL into a CodeMirror instance
+	cm.setValue("Fetching URL\n"+url+"\nPlease wait...");
+	buttonBlockers["fetchUrls"]++;
+	updateButtonState();
+	$.get(url, function (data) {
+			cm.setValue(data);
+		},'text').fail(function (jqXHR,textStatus,errorThrown) {
+			cm.setValue("Fetching URL\n"+url+"\nFailed!\n"+textStatus+"\n"+errorThrown);
+		}).always(function () {
+			buttonBlockers.fetchUrls--;
+			if (!buttonBlockers.fetchUrls)
+				delete buttonBlockers.fetchUrls;
+			updateButtonState();
 		});
-		params[paramSplit[0]] = paramSplit[1];
-		return params;
-	}, {});
 }
 
-function initialize (hash) {
-	console.log("hash", hash); //DB
+function setupOutputFile (fn, text) {
+	var found = $('div.outputs>.filename')
+		.filter(function(){ return $(this).text() == fn });
+	var cm;
+	if (found.length) {
+		var div = found.parent();
+		cm = div.data('CodeMirrorInstance');
+	}
+	else {
+		var div = $('<div/>',{class:"codewithfn outputs"});
+		div.append( $('<div/>',{class:"filename",text:fn}) );
+		var ta = $('<textarea/>').appendTo(div);
+		$('#outputhere').before(div);
+		cm = makeCM(ta,1,1);
+		div.data('CodeMirrorInstance', cm);
+	}
+	cm.setValue( text ? text : '' );
+}
+
+$(function () {
+	
+	var hashdata = window.location.hash.substr(1);
+	var hash = hashdata.length>0 ? JSON.parse(decodeURIComponent(hashdata)) : {};
+	
 	// script
-	if (hash["script"] || hash["scripturl"]) {
-		var script = $('#script');
-		script.show();
-		var cm = makeCM($('#perlcode'));
-		script.data('CodeMirrorInstance', cm);
+	var scriptdiv = $('#script');
+	if ( hash["script"] || hash["script_url"] ) {
+		scriptdiv.show();
+		var cm = makeCM($('#perlcode'),0,0);
+		scriptdiv.data('CodeMirrorInstance', cm);
 		if (hash["script"])
 			cm.setValue(hash.script);
-		else if (hash["scripturl"]) {
-			//TODO: fetch URL
-		}
+		else if (hash["script_url"])
+			fetchUrl(hash.script_url,cm);
 		else throw "internal error: this shouldn't happen";
-		if (hash["scriptfn"])
-			$('.filename',script).text(hash.scriptfn);
+		if (hash["script_fn"])
+			$('>.filename',scriptdiv).text(hash.script_fn);
 	}
-	if (hash["cmdline"]) {
+	
+	// command line
+	if (hash["cmdline"])
 		$('#argv').val(hash.cmdline);
-	}
+	
 	// input files
 	$('.inputs').remove();
-	for (var i=1;;i++) {
-		if (!( hash["i"+i+"f"] || hash["i"+i+"u"] )) break;
-		var fn = hash["i"+i+"n"] || "input"+i+".txt";
+	if ( hash["inputs"] ) hash.inputs.forEach(function(inp,i) {
+		var fn = inp["fn"] || "input"+(i+1)+".txt";
 		var div = $('<div/>',{class:"codewithfn inputs"});
 		div.append( $('<div/>',{class:"filename",text:fn}) );
 		var ta = $('<textarea/>').appendTo(div);
 		$('#inputhere').before(div);
 		var cm = makeCM(ta,1,0);
 		div.data('CodeMirrorInstance', cm);
-		if (hash["i"+i+"f"]) {
-			cm.setValue(hash["i"+i+"f"]);
-		}
-		else if (hash["i"+i+"u"]) {
-			//TODO: fetch URLs
-		}
-	}
+		if (inp["text"])
+			cm.setValue(inp.text);
+		else if (inp["url"])
+			fetchUrl(inp.url,cm);
+	});
+	
 	// stdout/stderr
-	if (hash["mergestdouterr"]) {
+	if (hash["mergeStdOutErr"]) {
 		mergeStdOutErr = 1;
 		$('#stdout>.filename').text("STDOUT+STDERR");
 	}
@@ -196,44 +234,53 @@ function initialize (hash) {
 		$('#stdout>.filename').text("STDOUT");
 	}
 	clearStdOutput();
-	// output files
-	for (var i=1;;i++) {
-		if (hash["o"+i+"n"]) {
-			var div = $('<div/>',{class:"codewithfn outputs"});
-			div.append( $('<div/>',{class:"filename",text:hash["o"+i+"n"]}) );
-			var ta = $('<textarea/>').appendTo(div);
-			$('#outputhere').before(div);
-			var cm = makeCM(ta,1,1);
-			div.data('CodeMirrorInstance', cm);
-		}
-		else break;
-	}
-}
-
-$(function () {
 	
-	initialize(parseParams(window.location.hash.substr(1)));
+	// output files
+	$('.outputs').remove();
+	if ( hash["outputs"] ) hash.outputs.forEach(function(outp) {
+		setupOutputFile(outp);
+	});
 	
-	var btn_runperl = $('#runperl');
-	btn_runperl.click( function () {
+	$('#runperl').click( function () {
 		clearStdOutput();
-		
+		var rp_data = {};
+		// command-line args
 		var argv = parseCmdLine($('#argv').val());
 		if (argv.length<1 || argv[0]!="perl") {
-			console.error("invalid command line");
-			return }
-		else argv.shift();
-		
-		var runperl = {
-			//TODO: input files
-			argv: argv,
-			//TODO: script: perl_cm.getValue(),
-		};
-		
-		btn_runperl.prop("disabled",true);
-		perlRunner.postMessage({ runPerl: runperl },'*');
+			$('#runnererrors>pre').text('Invalid command line, command must be "perl"');
+			$('#runnererrors').show();
+			return;
+		} // else
+		argv.shift();
+		rp_data.argv = argv;
+		$('#runnererrors>pre').text('');
+		$('#runnererrors').hide();
+		// script
+		if (scriptdiv.is(':visible')) {
+			rp_data.script = scriptdiv.data('CodeMirrorInstance').getValue();
+			rp_data.script_fn = scriptdiv.find('>.filename').text();
+		}
+		// inputs
+		$('.inputs').each(function () {
+			var div = $(this);
+			var fn = $('>.filename',div).text();
+			var text = div.data('CodeMirrorInstance').getValue();
+			if (!rp_data["inputs"]) rp_data.inputs = [];
+			rp_data.inputs.push([fn, text]);
+		});
+		// outputs
+		$('.outputs').each(function () {
+			var fn = $(this).find('>.filename').text();
+			if (!rp_data["outputs"]) rp_data.outputs = [];
+			rp_data.outputs.push(fn);
+		});
+		// send message to runner
+		buttonBlockers.runnerState = 1;
+		updateButtonState();
+		lastExitStatus = null;
+		runnerState("Requesting Perl Run...");
+		perlRunner.postMessage({ runPerl: rp_data }, '*');
 	});
-	btn_runperl.prop("disabled",true);
 	
 	findPerlRunner();
 });
@@ -255,6 +302,14 @@ $(function () {
 	<input type="text" id="argv" class="code" size="60" value='perl' />
 </div>
 
+<div id="runnerstate" class="text">
+	Loading...
+</div>
+
+<div id="runnererrors" style="display:none;">
+	<pre></pre>
+</div>
+
 <div id="stdout" class="codewithfn" style="display:none;">
 	<div class="filename">STDOUT</div>
 	<textarea></textarea>
diff --git a/web/democode/perlrunner.html b/web/democode/perlrunner.html
index 545a16a..baa7c8c 100644
--- a/web/democode/perlrunner.html
+++ b/web/democode/perlrunner.html
@@ -23,7 +23,7 @@ See the licenses for details.
 
 You should have received a copy of the licenses along with this program.
 If not, see http://perldoc.perl.org/index-licence.html
--->
+##### -->
 
 <!-- Possible To-Do for Later: This whole thing could probably also be
 	accomplished with a Web Worker, but that would probably require a
@@ -44,83 +44,124 @@ Perl.endAfterMain=true; // act like command-line perl
 
 var knownClients = [];
 var currentClient; // which client we're running Perl for, also keeps state
+var curOutputFiles;
+var stdbuf = [null,'',''];
+
+function reportErr (err) {
+	if (currentClient)
+		currentClient.postMessage({ perlRunnerError: err },'*');
+	else
+		console.error(err);
+}
 
 Perl.addStateChangeListener(function (from,to) {
 	if (from==to) return; // won't be needed as of v0.09-beta
-	for(var i=0; i<knownClients.length; i++)
-		knownClients[i].postMessage({ perlRunnerState: Perl.state },'*');
-	if (to=="Ended") {
-		if (currentClient) {
-			for (var c=1;c<=2;c++) // flush buffers
-				if (stdbuf[c].length)
-					currentClient.postMessage({ perlOutput: { chan:c, data:stdbuf[c] } },'*');
-			//TODO: how to handle nonzero exit codes and communicate them back to the client
-			//TODO: post output files
+	if (to=="Ended" && currentClient) {
+		for (var chan=1;chan<=2;chan++) // flush buffers
+			if (stdbuf[chan].length) {
+				currentClient.postMessage({ perlOutput: { chan:chan, data:stdbuf[chan] } },'*');
+				stdbuf[chan] = '';
+			}
+		currentClient.postMessage({ perlRunnerState: Perl.state,
+			exitStatus: Perl.exitStatus },'*');
+		for(var i=0; i<knownClients.length; i++)
+			if (knownClients[i]!=currentClient)
+				knownClients[i].postMessage({ perlRunnerState: Perl.state },'*');
+		if (curOutputFiles) {
+			var ofs = curOutputFiles.map(function (file) {
+				//TODO Later: Support binary files as well?
+				// {encoding:"binary"} => readFile returns Uint8Array
+				// Should then also provide the same support on FS.writeFile() as well
+				var of = { fn: file };
+				try {
+					of.text = FS.readFile(file, {encoding:"utf8"});
+				}
+				catch (e) {
+					reportErr("couldn't read "+file+" because "+e);
+				}
+				return of;
+			});
+			currentClient.postMessage({ perlOutputFiles: ofs },'*');
 		}
-		else console.error("state change to Ended with no current client?");
+	}
+	else {
+		for(var i=0; i<knownClients.length; i++)
+			knownClients[i].postMessage({ perlRunnerState: Perl.state },'*');
+	}
+	if (to=="Ended") {
+		if (!currentClient)
+			console.error("Internal Error: Perl state change to Ended with no client");
 		window.location.reload(false);
 	}
 });
 
-var stdbuf = [null,'',''];
 Perl.output = function (str,chan) {
 	stdbuf[chan] += str;
 	var pos = stdbuf[chan].lastIndexOf("\n");
-	if (pos>-1) {
-		var line = stdbuf[chan].slice(0,pos);
-		if (currentClient)
-			currentClient.postMessage({ perlOutput: { chan:chan, data:line+"\n" } },'*');
-		else
-			console.warn("output on",chan==1?"STDOUT":"STDERR",
-				"with no client?",line);
-		stdbuf[chan] = stdbuf[chan].slice(pos+1);
-	}
+	if (pos<0) return;
+	var lines = stdbuf[chan].slice(0,pos+1);
+	if (currentClient)
+		currentClient.postMessage({ perlOutput: { chan:chan, data:lines } },'*');
+	else
+		console.error("Internal Error: Output on",chan==1?"STDOUT":"STDERR","with no client:",lines);
+	stdbuf[chan] = stdbuf[chan].slice(pos+1);
 };
 
+function saveFile (fn, data) {
+	if (fn.substring(0,1)!='/') // if relative, make absolute
+		fn = FS.joinPath([FS.cwd(), fn]);
+	try {
+		FS.writeFile(fn, data);
+	}
+	catch (e) {
+		reportErr("couldn't write "+file+" because "+e);
+	}
+}
+
+window.addEventListener('message', function (event) {
+	if (event.data["perlRunnerDiscovery"]) {
+		if (!knownClients.includes(event.source))
+			knownClients.push(event.source);
+		event.source.postMessage({ perlRunnerState: Perl.state },'*');
+	}
+	else if (event.data["runPerl"]) {
+		if (!knownClients.includes(event.source))
+			knownClients.push(event.source);
+		// check state
+		if (currentClient && currentClient !== event.source) {
+			console.error("Attempt to run Perl from",event.source,
+				"but am already running Perl for",currentClient);
+			reportErr("Attempt to run Perl (from "+event.origin
+				+") but am already running Perl for someone else (see JavaScript console)");
+			return;
+		} // else
+		currentClient = event.source;
+		if (Perl.state!="Ready") {
+			reportErr("Attempt to run Perl in state "+Perl.state);
+			return;
+		} // else
+		// set up files and run perl
+		var rp = event.data.runPerl;
+		if (rp["script"]) {
+			var script_fn = 'script.pl';
+			if (rp["script_fn"])
+				script_fn = rp.script_fn;
+			saveFile(script_fn, rp.script);
+		}
+		//TODO Later: can we support STDIN? (probably need to look at webperl.js)
+		if (rp["inputs"])
+			rp.inputs.forEach(function (inp) {
+				saveFile(inp[0], inp[1]);
+			});
+		curOutputFiles = rp["outputs"];
+		Perl.start( rp["argv"] ? rp.argv : [] );
+	}
+	else console.warn("Perl Runner ignoring unknown message:", event.data);
+});
+
 Perl.init(function () {
+	Module['thisProgram'] = 'perl';
 	FS.currentPath = ENV.HOME; // NOTE: https://github.com/kripken/emscripten/issues/5873
-	window.addEventListener('message', function (event) {
-		var data = event.data;
-		var result;
-		if (data["perlRunnerRegisterClient"]) {
-			result = { perlRunnerState: Perl.state };
-			if (!knownClients.includes(event.source))
-				knownClients.push(event.source);
-		}
-		else if (data["runPerl"]) {
-			if (!knownClients.includes(event.source))
-				knownClients.push(event.source);
-			if (currentClient) {
-				//TODO Later: a way to communicate these errors back to client?
-				console.error("Attempt to run Perl from",event.source,
-					"but am already running Perl for",currentClient);
-				return;
-			}
-			if (Perl.state!="Ready") {
-				console.error("Attempt to run Perl in state",Perl.state,
-					"from",event.source);
-				return;
-			}
-			
-			currentClient = event.source;
-			
-			var scriptFn = data.runPerl["scriptName"]
-				? data.runPerl.scriptName : 'script.pl';
-			Module['thisProgram'] = './'+scriptFn;
-			FS.writeFile( FS.joinPath([FS.cwd(), scriptFn]),
-				data.runPerl.script );
-			
-			//TODO: input files
-			
-			var argv = data.runPerl["argv"] ? data.runPerl.argv : [scriptFn];
-			Perl.start(argv);
-		}
-		else console.warn("Perl Runner ignoring unknown message:", data);
-		//console.log("runner got message", data, "result", result); //DB
-		if (result)
-			event.source.postMessage(result,
-				event.origin==null || event.origin=="null" ? '*' : event.origin);
-	});
 });
 
 </script>
