Perl CGI + Bash script output in wrong order

h.chris has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks,

I'm new to perl and learning to develop my first Perl-CGI HTML page. I have a bash script that run few of the database functions within our organization, part of the script while performing different operations it does show a progress bar displaying (.)dots on the terminal

There is a requirement and now we want the script to be run from HTML page wherein our developers could use the webpage to run the script without actually connecting to the server. After investigating found Perl-CGI is a good option and Initially I had problem with perl based buffering while running the script through perl-CGI. However I fixed the issue following suggestions from other posts by using ($|=1;) to generate un buffered perl output.

After fixing the buffer issue, now I have 2 issues. please see below,

1) while I execute the perl script from terminal the output does display (.)dots, However they appear in wrong order....

2) If I execute from the webpage - output doesn't display (.)dots - however waits until it finishes the function + wrong order In order to help debugging the script - I made sample BASH and PERL to re-generate the same issue, I am attaching the BASH and Perl code here. Please see and advise if we can achieve OUTPUT displaying the progress bar and also in the correct order

Bash_Script: Name: shell_script.sh

#!/bin/bash

###
rundots() { ( trap 'exit 0' SIGUSR1;  while : ;  do echo -ne '.' >&2; 
+sleep 0.2; done) &  dotpid=$!; }
###
stopdots() { kill -USR1 $dotpid; wait $dotpid; trap EXIT; }
###
startdots() {
echo -e "\nExecuting function >>>> $(tr [a-z] [A-Z] <<< "${FUNCNAME[ 1
+ ]}") <<<<<"
              echo -ne "---->>Script executing, please wait"
              rundots; trap "stopdots" EXIT; return 0;
sleep 0.3}

###
main1() {
startdots
echo -e "display space usage" > /tmp/shell_script.log
sleep 4
du -sh * >> /tmp/shell_script.log
stopdots
}

main2() {
startdots
echo -e "list files," >> /tmp/shell_script.log
sleep 4
ls -lsrt >> /tmp/shell_script.log
stopdots
echo -e "\n\n*********** END OF THE BASH SCRIPT ************"
}

### call functions
main1
main2
[download]

Perl-CGI: Name: perl_script.pl

#!/usr/bin/perl -w
$|=1;
use CGI qw(:standard);
#use IO::Handle;
use FileHandle;
print "Content-type: text/html\n\n";
print '<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
        <title>Page title</title>
        <link rel="stylesheet" href="hari.css" type="text/css" media="
+screen">
</head>';
open (my $cmds, "/var/www/cgi-bin/shell_script.sh |");
open (my $LOG, '>', '/tmp/perl.log');
select((select($LOG), $|=1)[0]);
while (<$cmds>) {
#print "<pre>";
        print;
        print $LOG $_;
#print "</pre>";
}
close $cmds;
close $LOG;

print '
</body>
</html>';
[download]

Thanks in advance.

Comment on Perl CGI + Bash script output in wrong order Select or Download Code

Replies are listed 'Best First'.
Re: Perl CGI + Bash script output in wrong order by perlfan (Parson) on Jun 09, 2014 at 14:45 UTC
Dear God, please make sure you put some authentication and restricted IP in front of this. FWIW, you can just output HTTP headers via the bash script, you don't need to wrap that up into a Perl script. A CGI program can be anything. Also, please don't do it this way. You never want a direct URL to execute a script. Even if you have authentication locked down, you may accidentally call it when you really don't want to.	[reply]
Re^2: Perl CGI + Bash script output in wrong order by h.chris (Initiate) on Jun 09, 2014 at 15:00 UTC
Hi, Thanks for your suggestions, I did learn we can use BASH to output HTTP headers - however I want move away from bash, so thought this will be a good chance to start with. With regards to URL executing script - As I mentioned on my original post, this is just a sample script to re-generate the issue - Original script is NOT a direct URL based one ! *Please note: the scripts attached are just for debugging purpose Regards,	[reply]
Re^3: Perl CGI + Bash script output in wrong order by jeffa (Bishop) on Jun 09, 2014 at 15:02 UTC
I recommend going through Ovid's CGI Course. jeffa L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR B--B--B--B--B--B--B--B-- H---H---H---H---H---H--- (the triplet paradiddle with high-hat)	[reply] [d/l] [select]
Re: Perl CGI + Bash script output in wrong order by neilwatson (Priest) on Jun 09, 2014 at 15:26 UTC
I've never been in situation where use strict and use warnings did not help me reach my end goal. Try them. http://www.perlmonks.org/?node_id=87956 Neil Watson watson-wilson.ca	[reply]
Re: Perl CGI + Bash script output in wrong order by h.chris (Initiate) on Jun 10, 2014 at 14:24 UTC
Hi Thanks everyone, I fixed the problem. It is do with "\|" while executing the bash script Regards, Hari	[reply]
Re^2: Perl CGI + Bash script output in wrong order by Anonymous Monk on Sep 16, 2014 at 08:58 UTC
Hi Hari, I am in a similar situation and would request your help. can you please elaborate on how did you fix the issue? Thanks RS	[reply]