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titleAnswer...

The cutadapt usage says that output can be written to a file using the -o option

    cutadapt -a ADAPTER [options] [-o output.fastq] input.fastq

But the brackets around [-o output.fastq] suggest this is optional. Reading a bit further we see:

... Without the -o option, output is sent to standard output.

This suggests output can be specified in 2 ways:

  • to a file, using the -o option
    • cutadapt -a CGTAATTCGCG -o trimmed.fastq  small.fq
  • to standard output without the -o option
    • cutadapt -a CGTAATTCGCG small.fq > 1> trimmed.fastq

Where does cutadapt read its input from by default? How can that be changed? Can the input FASTQ be in compressed format?

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titleAnswer...

The cutadapt usage says an input.fastq file is a required argument:

    cutadapt -a ADAPTER [options] [-o output.fastq] input.fastq

But again, reading a bit further we see:

Input may also be in FASTA format. ...                           Compressed input and output is supported and
auto-detected from the file name (.gz, .xz, .bz2). Use the file name '-' for
standard input/output. Without the -o option, output is sent to standard output.

This suggests input can be specified in 2 ways:

  • from a file, using the -o option
    • cutadapt -a CGTAATTCGCG -o trimmed.fastq  fastq  small.fq
  • from standard input if the input.fastq argument is replaced with a dash ( - )
    • cat small.fq | cutadapt -a CGTAATTCGCG -o trimmed.fastq  fastq  -

And also says that the input.fastq file can be provided in one of three compression formats.

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