converting fasta to fastq

[keecarter]

I am attempting to convert my fasta files to fastq using the command:
seq -F contig.2.fasta > contig.2.fq

but I keep getting:
seq: invalid option -- F

[Wei Shen]

seq: invalid option -- F

This is the seq command from the system.

The right way is

seqtk seq -F G      contig.2.fasta > contig.2.fq

[keecarter]

So I am getting an fq file, but it is empty.