perl - get print to print *now* in cgi script (hard to explain).

Linicks · 12-13-2015, 10:48 AM

Hi Guys and Gals,

Been a Slack user for over 12 years, and this has me beat.

I have a web form that some fields drive a binary to produce results, and other fields just grep a file for results.

Now, one field when used can take a few seconds to process, so if I put a:

print "This can take a seconds...";

before the backticks line, it doesn't print UNTIL the backticks command has finished?

Yet, if the previous functions in my code are run and print, it does print first and then waits for the backticks command.

So, something like this pseudo code works:

if (match) { # true

grep file;

print $results;

}

if (match) {

print "Please wait, can take a few seconds";

$var=`command'

print $results;

}

Which then runs the output from the first match, and then prints the 'Please wait...' line as the backticks command processes.

But IF the first match is false, the 'Please wait...' line doesn't get printed until the backticks command is finished, so it all gets printed at the same time, and the user sits looking at a 'loading...' thing in their browser.

Hope you understand what I mean, and thanks for any help why this happens/what is going on.

Nick

Aia · 12-13-2015, 01:08 PM

pseudo code

Code:

display "Please wait, it can take a few seconds"
if true
   execute command
   display result of command
else
   display result of failure

Linicks · 12-13-2015, 02:06 PM

Already tried that, and various variations of it. None work, but some do.

It's like something just ignores it depending on what matches before it.

Why (as a standalone):

if (match) {

print "Please wait..."

$var=`command`;

print $var;

}

Doesn't output the first 'print' straight away, I don't know.

Nick

norobro · 12-13-2015, 03:02 PM

A linefeed should flush the output buffer.

Code:

print "Please wait...\n"

If you can't live with that you need to turn on autoflushing (link).

Linicks · 12-14-2015, 10:54 AM

Thank you! This works great:

#!/usr/bin/perl -w $|++;

Nick

Linicks · 12-14-2015, 12:15 PM

Actually, this isn't solved - sometimes it works, sometimes it doesn't and everything gets printed at once after a delay.

I am wondering if it is the browser doing something funny and just waits.

Nick

Ramurd · 12-24-2015, 08:14 AM

The webserver may buffer as well... it probably does, so you have to tell your webserver not to buffer.

Searched on the interwebs for this issue on Apache HTTPD server with php... and this was one solution:

Code:

SetEnvIfNoCase Request_URI \.cgi$ no-gzip dont-vary

you may have to change .cgi to something else, like .pl or so...