in reply to change \n to \t
$ echo "1.fa >1 AGTCGTAGCAT >2 TGAGCTACG >3 GGCATAGN >4 CGCACNCAGCTACACC >5 NGATAGCTACA " | perl -pe'$_ .= "\t" if s/^>\S+\K\s+$//' 1.fa >1 AGTCGTAGCAT >2 TGAGCTACG >3 GGCATAGN >4 CGCACNCAGCTACACC >5 NGATAGCTACA
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