bedtool intersect multiple bed files

Question

I have 7 biological replicate of a normal sample after peak-calling I converted it into bed files and now I want to find what are the common region between those .

So i tried with bedtool intersect

my command is this 
bedtools intersect -a SRR2920506.filtered.bed -b SRR2920531.filtered.bed SRR2920466.filtered.bed SRR2920478.filtered.bed SRR2920507.filtered.bed SRR2920532.filtered.bed  > answer.bed

it says " the intersect tool can detect overlaps between a single -a file and multiple -b files (instead of just one previously). One simply provides multiple -b files on the command line."

My doubt is the file that goes to "a" argument is not query which i have to detect overlaps against "b" files as these are all biological replicate. Am i doing the right way?

Secondly I tried with bedops but the number of overlaps which is reported is really low when i compare the result which i get from bedtools intersect function.

Any suggestion or help regarding how to intersect multiple would be really appreciated

Answer 1

If you want to find the intersection between ALL your bedfiles, you can try multiIntersectBed (available since bedtools 2.14.3).

It should work like this :

multiIntersectBed -i SRR2920506.filtered.bed SRR2920531.filtered.bed SRR2920466.filtered.bed SRR2920478.filtered.bed SRR2920507.filtered.bed SRR2920532.filtered.bed  > answer.bed

To sort your bedfiles by chromosome then by start :

sort -k 1,1 -k2,2n myfile.bed