I carefully read your code and made a few tweaks to it. You are making a good start. Read and reread the docs, ask questions and keep working at it. I strongly recommend that you take the time to understand regexes. They are a very, very, useful and powerful tool.

I noticed some problems with your code as I read it.

• You have inconsistent use of inclusive vs exclusive comparisons.
• Your algorithm for floating point validation would allow numbers like '12. 3' (that's a space between the . and the 3) to pass.
• There are a number of variables that seem to come from nowhere. Are they globals?
• You are using C style for loops.

For loops in perl are usually done as follows:

# You had
for ($l_count = 1; $l_count < $l_len; $l_count++)
{
$lower=$lower."9";
}

# Try this instead:
for my $l_count ( 1..$l_len ) {
    $lower=$lower."9";

}

# To build up a string like this you should be using the 'x' operator
my $lower = '9' x $l_len;
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Here's your code with my tweaks applied. What follows is untested, but should work.

use constant MATCH => 1;  # Return value for good match
use constant FAIL  => 0;  # Retrun value for failed match

use constant MIN   => 0;  # Index of minimum value for integer checks
use constant MAX   => 1;  # Index of maximum value for integer checks

############# SUB-ROUTINE TO CHECK FOR INTEGER TYPE ##############

#check for small int, big int and int data types and return a 0 if cor
+rect

# else return a 1

sub int_chk {
    my $input     = shift;
    my $data_type = shift;  # Where was this coming from in your code?

    $input = $input+0;

    # Test for integerness
    if ( $input != int( $input ) ) {
        return FAIL;
    }

    # Use a hash lookup to simplify your code.
    my %check = (   # type                         MIN                
+  MAX
        SMALLINT => [               -32768,               32767 ],
        INTEGER  => [          -2147483648,          2147483647 ],
        BIGINT   => [ -9223372036854770000, 9223372036854770000 ],
    );

    # Test for range
    if ( exists $check{$data_type} ) {

        my $match = (
            $input >= $check{$data_type}[MIN] # I used inclusive range
+s here
                and 
            $input <= $check{$data_type}[MAX] 
        ) ? MATCH : FAIL;

        return $match;
    }
    else {
        return FAIL;
    }

    die "Unreachable code executed";
}

sub decimal_chk {
    my $input = shift;
    my $whole_places   = shift || 3;  # Set a default value
    my $decimal_places = shift || 2;  # for each of these args

    return $input =~ /
        ^                           # Start of input
        -?                          # Optional minus sign
        \d{0,$whole_places}         # 1-? whole number digits
        (
            \.                      # Manadatory decimal point
            \d{0,$decimal_places}   # 1-? decimal places
        )?                          # decimal section is optional
        $                           # End of input
    /x ? MATCH : FAIL ;     # x modifier allows comments and whitespac
+e

}
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