#!/bin/awk -f

BEGIN {
    FS  = "";
}

value ~ "MYVALUE" # silly test
{
    print "1 - " substr($0, 235, 12);
}

$235 ~ "M" {
    print "2 - " substr($0, 235, 12);
}

{
    if(value == substr($0, 235, 12))
    {
        print "3 - " substr($0, 235, 12);
    }
    if(match(value,substr($0, 235, 12)))
    {
        print "4 - " substr($0, 235, 12);
    }
}

END {
    print "exit"
}

$ ls -l  $(which awk)
lrwxrwxrwx 1 root root 4 Jul 10  2015 /bin/awk -> gawk
$ gawk --version
GNU Awk 3.1.5

$235 ~ "M"
{
    print "2 - " substr($0, 235, 12);
}

$235...$247 ~ value

#!/usr/bin/python

import re

t   = 'ABC'
rg  = '^.{235,235}' + t
rgx = re.compile(rg)
tt  = '00000ABC00'
if(rgx.match(tt)):
    print "OK"
else:
    print "KO"

{
    if(substr($0, 235, 12) ~ value)
    {
        print "4 - " substr($0, 235, 12)
        next
    }
    else
    {
        print "4 - NOK"
        next
    }
}

$235, $247 ~ value { ... action here ... }

substr($0, 235, 12) ~ value { ... action here ... }

$235 ~ "M" {  print "2 - " substr($0, 235, 12);  }

$235 ~ "M"
{  print "2 - " substr($0, 235, 12);  }

BEGIN { FS="" }
# oursubstr will be updated first for each record.
{ oursubstr = substr($0, 235, 12) }
oursubstr ~ value { ... action ... }
...