Stop grep after one result on Solaris

Here's a different approach. I have a little Perl script which I have already posted in another answer that will highlight the user provided patterns in different colors. A slightly modified version of the script will act like grep:

#!/usr/bin/env perl
use Getopt::Std;
use strict;
use Term::ANSIColor; 

my %opts;
getopts('hic:l:',\%opts);
    if ($opts{h}){
      print<<EoF; 
Use -l to specify the pattern(s) to highlight. To specify more than one 
pattern use commas. 

-l : A Perl regular expression to be colored. Multiple expressions can be
     passed as comma separated values: -l foo,bar,baz
-i : makes the search case sensitive
-c : comma separated list of colors;

EoF
      exit(0);
    }

my $case_sensitive=$opts{i}||undef;
my @color=('bold red','bold blue', 'bold yellow', 'bold green', 
       'bold magenta', 'bold cyan', 'yellow on_blue', 
       'bright_white on_yellow', 'bright_yellow on_red', 'white on_black');
if ($opts{c}) {
   @color=split(/,/,$opts{c});
}
my @patterns;
if($opts{l}){
     @patterns=split(/,/,$opts{l});
}
else{
    $patterns[0]='\*';
}

# Setting $| to non-zero forces a flush right away and after 
# every write or print on the currently selected output channel. 
$|=1;

while (my $line=<>) 
{ 
    my $want=0;
    for (my $c=0; $c<=$#patterns; $c++){
    if($case_sensitive){
        if($line=~/$patterns[$c]/){
           $line=~s/($patterns[$c])/color("$color[$c]").$1.color("reset")/ge;
           $want++;
        }
    }
    else{
        if($line=~/$patterns[$c]/i){
          $line=~s/($patterns[$c])/color("$color[$c]").$1.color("reset")/ige;
          $want++;
        }
      }
    }
print STDOUT $line if $want>0;
}

If you save that script as cgrep somewhere in your PATH and make it executable, you can specify up to 10 different patterns, each of which will be printed in a different color:

$ cgrep -h
Use -l to specify the pattern(s) to highlight. To specify more than one 
pattern use commas. 

-l : A Perl regular expression to be colored. Multiple expressions can be
     passed as comma separated values: -l foo,bar,baz
-i : makes the search case sensitive
-c : comma separated list of colors;

I'm guessing that you probably have a file or directory called debug in your current working directory:

 $ ls -l
total 8
-rw-r--r--   1 jay   wheel   58 Feb  1 05:01 T
 $ grep [D]ebug T
    1 Debug
 $ grep [Dd]ebug T
    1 Debug
    2 debug

 $ touch debug
 $ ls -l
total 8
-rw-r--r--  1 jay  wheel  58 Feb  1 05:01 T
-rw-r--r--  1 jay  wheel   0 Feb  1 05:05 debug

 $ grep [D]ebug T
    2 debug
 $ grep [Dd]ebug T
    2 debug

I commend you on this excellent illustration why you must always escape shell metacharacters.

Update to clarify what's going on: I'm assuming you, like I, are using an OS with a case-insensitive filesystem (e.g. a Mac). When you execute the command, your shell performs a number of expansions on it before actually executing grep. One of those is filename expansion in which square brackets provide alternations:

[Dd]ebug on a case-sensitive filesystem would expand to either Debug debug, Debug or debug depending on what files it could match. Since it only matched the file debug, your command became:

grep debug T

If you remove that file and do touch Debug, you'll see the output of your command change because it will be interpolated as

grep Debug T

Without the debug file in your directory, your shell tries to interpolate the brackets but fails without a match so it happens to pass the argument through unchanged.