unfasta - FASTA without the pesky line breaks
Unfasta is a suite of command-line utilities for working with FASTA sequence data in the common “pipes and filters” style of Unix and GNU. The unfasta ‘file format’ is FASTA without line breaks in sequences. Unfasta files are valid FASTA, but suitable for stream processing.
Read more about unfasta here or at its source code repository https://github.com/zwets/unfasta. Unfasta is free and open source software released under GPL v3+.