no problem!! round robin is fine - here is a way I have done it in a liner without having to read the entire file into mem (just an example) :

# Choose first N FASTA records
perl -ne 'BEGIN {$/=">";$o=0}{chomp;$o<N?(/^$/?next:print">$_"):last;$
+o++}' EXAMPLE.fa
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example usage:

 perl -ne 'BEGIN{$/=">";$o=0}{chomp;$o<22?(/^$/?next:print">$_"):last;
+$o++}' b4x_est100.fa # print the first 22 records
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