Do all the keys which do not have "=" appear at the beginning of the string ?

Yes Buddy, fortunately, its only in beginning and that too only single string.

OK try

#!perl
use strict;
use Data::Dumper;
my $str = 'eab12345 a b c id=00000 x= pgrp=abc=defgh groups=abcdefgh a
+nd more roles=';
my @f = split / (\w+=)/,$str;

my @array = ();
while (@f){
  my $k = shift @f;
  if ($k =~ /=$/){
    my $v = shift @f;
    push @array,"$k$v";
  } else {
    # key no equal
    push @array,"$_=" for split /\s+/,$k;
  }
}
print Dumper \@array;
[download]

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1207515

use strict;
use warnings;

$_ = <<END;
eab12345 id=00000 pgrp=abcdefgh groups=abcdefgh home=/home/eab12345 sh
+ell=/usr/bin/ksh gecos=AB/C/Y0000/ABC/XYZ RTYUI, LMNOP *CONTRACTOR* (
+AS 00000) auditclasses=general,files,TCPIP login=true su=true rlogin=
+true daemon=true admin=false sugroups=ALL admgroups= tpath=nosak ttys
+=ALL expires=0 auth1=SYSTEM auth2=NONE umask=00 registry=AD SYSTEM=AD
+ logintimes= loginretries=5 pwdwarntime=5 account_locked=false minage
+=0 maxage=13 maxexpired=0 minalpha=1 minother=1 mindiff=1 maxrepeats=
+2 minlen=8 histexpire=13 histsize=8 pwdchecks= dictionlist=/abc/def/g
+hi/jkl default_roles= fsize=-1 cpu=-1 data=-1 stack=65536 core=000000
+ rss=65536 nofiles=2000 time_last_login=1512632113 time_last_unsucces
+sful_login=1505304923 tty_last_login=ssh tty_last_unsuccessful_login=
+ssh host_last_login=0.000.000.000 host_last_unsuccessful_login=0.000.
+000.000 unsuccessful_login_count=0 roles=
END

my @answers = /(?|^(\S+)|([^\s=]+=[^=\n]*)(?=\s))/g;

use Data::Dump 'pp';
pp \@answers;
[download]