I modified your problem definition into:

How to split a string into several substrings (of a given maximum length) without breaking a word when splitting.

I found this (quickly hacked) solution:

#! /opt/perl/bin/perl
use strict;
use warnings;

my $text = "Hello, I am a perl/mysql programmer, but am self taught so
+ I do not know all the awesome features Perl has, however, I am ok at
+ it though, I guess.";

sub split_at {
    my ( $text, $len ) = @_;
    my @result;

    my @parts = split /[ ]/, $text;

    my $short = shift @parts;
    while ( @parts ) {
        if ( length($short) + length($parts[0]) < $len ) {
            $short = join( ' ', $short, shift @parts );
        }
        else {
            push @result, $short;
            $short = shift @parts;
        }
    }

    push @result, $short;

    return @result;
}


{
    local $, = local $\ = $/;
    print split_at( $text, 100 );

    # beware
    print split_at( 'a'x110, 100 );
}
[download]

Limitation: If the given string doesn't contain any whitespace (\x20), it won't split at all.

If you just want/need the first substring, just use the first returned element.

Updates: