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fastx_mask command
 
The fastx_mask command performs low-complexity masking of sequences in a FASTA or FASTQ file.

The ‑qmask option specifies the masking algorithm to use. Default is fastnucleo or fastamino.

Output is written to -fastaout (FASTA) and/or -fastqout (FASTQ). If the input file is FASTA, then you cannot use -fastqout because the base quality scores are not known.

By default, soft masking is used (lower-case). The ‑hardmask option can be used to specify hard masking (overwrite Ns for nucleotids, Xs for amino acids).

The min_unmasked_pct option specifies the minimum fraction of the sequence that is not masked. If a larger fraction is masked, the sequence is discarded.

The max_unmasked_pct option specifies the maximum fraction of the sequence that is not masked. If a smaller  fraction is maskd, the sequence is discarded. The typical use of this option is to determine which sequences were discarded by min_unmasked_pct.

Multithreading is supported.

Example

usearch -fastx_mask reads.fastq -fastqout masked.fastq -qmask dust -min_unmasked_pct 50