This is a puzzle of a cross-domain fashion in multiple environments.
Problem: an Perl installation script that installs a Perl program that auto-starts at boot, and can be started or stopped from the command line. In any release of RHEL, CentOS, Debian, Ubuntu, or Kali.

I have found a bash script that seems to reliably identify 'system5-init', 'upstart', and 'systemd' as foundations for process control. Running the script in back-ticks has interpretation problems. Using 'system' will only return the exit value, not the STDOUT (which is possibly usable, but rather opaque). 

#create the bash script to determine whic Init System
  my $tmpScript = "/tmp/whichSysInit";
  my $whichInit = <<"END";
      #!/bin/bash
      if [[ `/sbin/init --version 2>/dev/null` =~ upstart ]]; then 
          echo using upstart;
      elif [[ `systemctl` =~ -\.mount ]]; then 
          echo using systemd;
      elif [[ -f /etc/init.d/cron && ! -h /etc/init.d/cron ]]; then 
          echo using sysv-init;
      else echo cannot tell; 
      fi

END

  open  OPT, "> $tmpScript";
  print OPT $whichInit;
  close OPT;
  chmod 0555, $tmpScript;

  #run that script to get answer
  my $rslt= `$tmpScript`;
  #unlink $tmpScript; # cleanup

  print " Initialization is $rslt\n";

  #react to the result
  #if ($rslt =~/using\s(?<si>\S+)/){
  #  my $sysInit= $+{si};

[download]
When I run the file left in /tmp/ from the command line, it echos the appropriate string.
When run the file in back-ticks the following errors are produced: 
/tmp/whichSysInit: 2: /tmp/whichSysInit: [[: not found
/tmp/whichSysInit: 1: /tmp/whichSysInit: systemctl: not found
/tmp/whichSysInit: 4: /tmp/whichSysInit: [[: not found
/tmp/whichSysInit: 6: /tmp/whichSysInit: [[: not found
Can not determine System Init mechanism <>.
 Exiting

[download]
I searched for the program '[[', but none was found.
Linux ubuntu 3.11.0-26-generic #45~precise1-Ubuntu SMP Tue Jul 15 04:02:35 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

The shell in the environmant is '/bin/bash'
Maybe the '#!' on line 1 isn't run? And bash isn't what is interpreting the script?
Thoughts?

It is always better to have seen your target for yourself, rather than depend upon someone else's description.

In reply to Back-ticks and bash by Wiggins

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