One of the easiest conversions is to convert a tab file to fasta. Reverse is also true except that some times sequences are in multiple lines and can cause issues in format conversion.

Following is an example tab file to try on:

seq1    atgc
seq2    gcta
seq3    agtcg

Let’s list the methods to convert

$ seqkit -w 0 tab2fx <input.fa> -o <output.fa(.gz)>
$ awk -v OFS="\n" '{print ">"$1,$2}' test.txt
$ awk -v OFS="\n" '{$1=">"$1}1' test.txt
$ sed  's/^/>/;s/\t/\n/' test.txt 
$ sed -r 's/^(.*)\t(.*)/>\1\n\2/' test.txt
$ parallel --colsep '\t' echo '\>'{1}'\\n'{2} :::: test.txt
$ while IFS=$'\t' read i j ; do echo ">"$i"\n"$j ; done < test.txt