How to pipe awk of bed file into samtools to extract fasta sequences?

Question

[mrj]

I have a bed file (seq.bed) that contains "queryID queryStart queryEnd". Following is the example (the content of seq.bed file).

SRR5892231.6 28 178

SRR5892231.7 4 307

SRR5892231.7 16 307

SRR5892231.9 216 408

I would like to extract out sequences that have at least 100bp in their upstream regions. if I use the following awk,

awk 'OFS="\t" {print $1, $2-100, $2}' seq.bed

how can i use pipe to send the output to samtools for "samtools faidx seq.fna queryID:queryStar-queryEnd"?

Could you please help me figure out how to pass $1, $2-100, and $2 for samtools faidx seq.fna queryID:queryStar-queryEnd?

Answer 1

[alex.zaccaron]

Piping to bedtools would be more straightforward:

awk 'OFS="\t" {if($2<100) print $1,"0",$2; else print $1, $2-100, $2}'  seq.bed | \
bedtools getfasta -fi seq.fasta -bed stdin

But if samtools is required, I would use a for loop:

awk '{if($2<=100) print $1":1-"$2; else print $1":"$2-100"-"$2}'  seq.bed  | while read LOCUS; do
   samtools faidx seq.fasta $LOCUS
done

[mrj]

Alex, this is great. Thank you very much.