title: Replace values only if they are different
body: <p>I have a vcf file like this:
  <a href="http://www.1000genomes.org/node/101" rel="nofollow">http://www.1000genomes.org/node/101</a></p>
  
  <p>Here's the example from that site:</p>
  
  <pre><code>##fileformat=VCFv4.0
  ##fileDate=20090805
  ##source=myImputationProgramV3.1
  ##reference=1000GenomesPilot-NCBI36
  ##phasing=partial
  ##INFO=&lt;ID=NS,Number=1,Type=Integer,Description="Number of Samples With Data"&gt;
  ##INFO=&lt;ID=DP,Number=1,Type=Integer,Description="Total Depth"&gt;
  ##INFO=&lt;ID=AF,Number=.,Type=Float,Description="Allele Frequency"&gt;
  ##INFO=&lt;ID=AA,Number=1,Type=String,Description="Ancestral Allele"&gt;
  ##INFO=&lt;ID=DB,Number=0,Type=Flag,Description="dbSNP membership, build 129"&gt;
  ##INFO=&lt;ID=H2,Number=0,Type=Flag,Description="HapMap2 membership"&gt;
  ##FILTER=&lt;ID=q10,Description="Quality below 10"&gt;
  ##FILTER=&lt;ID=s50,Description="Less than 50% of samples have data"&gt;
  ##FORMAT=&lt;ID=GT,Number=1,Type=String,Description="Genotype"&gt;
  ##FORMAT=&lt;ID=GQ,Number=1,Type=Integer,Description="Genotype Quality"&gt;
  ##FORMAT=&lt;ID=DP,Number=1,Type=Integer,Description="Read Depth"&gt;
  ##FORMAT=&lt;ID=HQ,Number=2,Type=Integer,Description="Haplotype Quality"&gt;
  #CHROM POS     ID        REF ALT    QUAL FILTER INFO                              FORMAT      NA00001        NA00002        NA00003
  20     14370   rs6054257 G      A       29   PASS   NS=3;DP=14;AF=0.5;DB;H2           GT:GQ:DP:HQ 0|0:48:1:51,51 1|0:48:8:51,51 1/1:43:5:.,.
  20     17330   .         T      A       3    q10    NS=3;DP=11;AF=0.017               GT:GQ:DP:HQ 0|0:49:3:58,50 0|1:3:5:65,3   0/0:41:3
  20     1110696 rs6040355 A      G,T     67   PASS   NS=2;DP=10;AF=0.333,0.667;AA=T;DB GT:GQ:DP:HQ 1|2:21:6:23,27 2|1:2:0:18,2   2/2:35:4
  20     1230237 .         T      .       47   PASS   NS=3;DP=13;AA=T                   GT:GQ:DP:HQ 0|0:54:7:56,60 0|0:48:4:51,51 0/0:61:2
  20     1234567 microsat1 GTCT   G,GTACT 50   PASS   NS=3;DP=9;AA=G                    GT:GQ:DP    0/1:35:4       0/2:17:2       1/1:40:3
  </code></pre>
  
  <p>After the header lines, each line has fields that contain genotypes starting with the 10th field. The 10th field is below the <code>NA0001</code> heading; the 11th field is genotype <code>NA0002</code>, etc. I have a file with 123 different genotypes, so going from position 10 to 133 (NA0001 until NA0123). What is shown in these fields can be 0/0, 0/1, 0/2 .... till 8/9 for instance. Now I want to replace all the non-equal ones. So I would like to keep 0/0, 1/1, 2/2, etc. And replace 0/1, 0/2, 1/2, 4/5, 4/6 etc by ./.</p>
  
  <p>I would like to write this in a C script. Thought about using sed y/regexp/replacement/ but no idea how to write all those unequal values in a regular expression. And on other positions in the file there could also be these values, so really only positions 10 till 133 should be replaced. And it needs to be replaced; I will be needing the rest of the file with the new values. </p>
  
  <p>Hope it is clear. Anyone any idea how to do this? </p>