awk - Introduce a new line before every row containing a specific word in linux -

i new linux. have tab delim text file following

a1 title body.1 gene a1 head head.1  head a1 trunk trunk.1 trunk a1 tail tail.1 tail a2 title body.2 gene a2 head head.2 head a2 trunk trunk.2 trunk a2 tail tail.2 tail a3 title body.3 gene a3 head head.3 head a3 trunk trunk.3 trunk a4 title title.4 gene a4 trunk trunk.4 trunk a4 tail tail.4 tail 

i introduce new line before every row containing word "gene" in last column following:

a1 title body.1 gene a1 head head.1  head a1 trunk trunk.1 trunk a1 tail tail.1 tail  a2 title body.2 gene a2 head head.2 head a2 trunk trunk.2 trunk a2 tail tail.2 tail  a3 title body.3 gene a3 head head.3 head a3 trunk trunk.3 trunk  a4 title title.4 gene a4 trunk trunk.4 trunk a4 tail tail.4 tail 

i tried following command

sed 's/gene/\ \n&\g' file.txt 

but introduces new line after row containing word "gene".

it great if 1 guide me how introduce new line before row containing word "gene" in last column.

you want (extended regex syntax):

$ sed -r 's/(^.*?\tgene$)/\n\1/' example  a1  title   body.1  gene a1  head    head.1  head a1  trunk   trunk.1 trunk a1  tail    tail.1  tail  a2  title   body.2  gene a2  head    head.2  head a2  trunk   trunk.2 trunk a2  tail    tail.2  tail  a3  title   body.3  gene a3  head    head.3  head a3  trunk   trunk.3 trunk  a4  title   title.4 gene a4  trunk   trunk.4 trunk a4  tail    tail.4  tail 

in regex can see:

1. a substitution command 's/.../.../'
2. capture group of whole line ends tab character , gene: (^.*?\tgene$).
3. inserting newline character , captured group (first , only) result: \n\1

please note there catch in question:

i introduce new line before every row containing word "gene" in last column

this leads assumption need result's first line empty (or single newline precise)

however example's first line not preceded empty line. if need, should use sed addressing:

pono@pono-carbon:~$ sed -r '2,$s/(^.*?\tgene$)/\n\1/' example a1  title   body.1  gene a1  head    head.1  head a1  trunk   trunk.1 trunk a1  tail    tail.1  tail  a2  title   body.2  gene a2  head    head.2  head a2  trunk   trunk.2 trunk a2  tail    tail.2  tail  a3  title   body.3  gene a3  head    head.3  head a3  trunk   trunk.3 trunk  a4  title   title.4 gene a4  trunk   trunk.4 trunk a4  tail    tail.4  tail