Remove repeated ALT allele from the REF field of a vcf-like file I have 200 .txt files on a Linux system. In each file, I have the reference allele in the REF column and INDELs in the ALT column.
Let's say I have A in the REF column and AC in the ALT. I want to remove  the A from the ALT column because that is a repetition of the A reference allele. For example, if I have C in the REF column and CCAT in the ALT column, I only want CAT to remain in the ALT column.

This is what my files look like

CHROM   REF ALT
chr1    C   CT
chr1    C   CT
chr1    C   CA
chr1    C   CT


Can someone help me please?

Solution from @Terdon

This is my original file

#CHROM  POS ID  REF ALT
chr4    5708160 .   G   GATAAC
chr4    30280292    .   C   CACGTAT
chr6    166253422   .   C   CCTTTCT
chr11   21931340    .   A   AACACACGC


This is what happened after running your kindly suggestion 

[fi1d18@cyan01 indel]$ awk -F"\t" -vOFS="\t" '{ if(substr($5,1,1) == $4){$5=substr($5,4); }}1' indels.vcf &gt; out.vcf

#CHROM  POS ID  REF ALT
chr4    5708160 .   G   AAC
chr4    30280292    .   C   GTAT
chr6    166253422   .   C   TTCT


I think more than one allele being removed from ALT column, is not it?
I am making a couple of assumptions here: 


the delimiter is tab
the reference allele is always present in the ALT column
the reference allele in the ALT column is always in the first position


With those in mind, you can do this using awk as follows: 

awk 'BEGIN{FS="\t";OFS="\t"}{$3=substr($3,2)}{print $0}'


Update 1: Using the new VCF style file that @Angel provided, here's how I would do it. This is not significantly different from what @terdon proposed below. The code below will work even if the reference allele is >1 nt.

$ cat test.vcf
#CHROM  POS     ID      REF     ALT
chr4    5708160 .       G       GATAAC
chr4    30280292        .       C       CACGTAT
chr6    166253422       .       C       CCTTTCT
chr11   21931340        .       A       AACACACGC

$ awk 'BEGIN{FS="\t";OFS="\t"}{l=length($4); if ($4==substr($5,1,l)) {$5=substr($5,l+1); print $0} else {print $0}}' test.vcf
#CHROM  POS     ID      REF     ALT
chr4    5708160 .       G       ATAAC
chr4    30280292        .       C       ACGTAT
chr6    166253422       .       C       CTTTCT
chr11   21931340        .       A       ACACACGC