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These are 101-base reads. wc -c counts the "invisible" newline character, so subtract 1 from the character count it returns for a line.

Here's a way to strip the trailing newline characters from the quality scores string before calling wc -c to count the characters. We use the echo -n option that tells echo not to include the trailing newline in its output. We gemerate generate that text using sub-shell evaluation (an alternative to backtick evaluation) of that zcat ... command:

echo -n $( zcat Sample_H54_miRNA_L004_R1.cat.fastq.gz | head -2 | tail -1 ) | wc -c

The cutadapt --help output describes its usage as follows:

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

From this we see that the input.fastq is a required argument. Clearly, it can be a FASTQ file, and it can be compressed based on this help:

Compressed input and output is supported and
auto-detected from the file name (.gz, .xz, .bz2).
Use the file name '-' for standard input/output.

And this says that input reads can also be provided on standard input, if that argument is a hyphen ( - ). So input data can come:

• from a file named as an argument:
  
  • cutadapt -a CGTAATTCGCG -o small.trim.fq  small.fq
  • and that input.fastq file can be provided in one of three compression formats
• from standard input if the input.fastq argument is replaced with a dash ( - )
  
  • cat small.fq | cutadapt -a CGTAATTCGCG -o small.trim.fq  -
    

What about cutadapt output (the trimmed reads)? The brackets around the usage -o option indicate that the resulting trimmed FASTQ can be written to a file, but is not by default. This implies that cutadapt by default writes its results to standard output. So output can go

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

Finally, as we've seen, cutadapt also writes diagnostic output. Where does it go? The usage line doesn't say anything about diagnostics explicitly. But in the Output section of cutadapt --help:

   -o FILE, --output=FILE
        Write trimmed reads to FILE. FASTQ or FASTA format is
        chosen depending on input. The summary report is sent
        to standard output. Use '{name}' in FILE to
        demultiplex reads into multiple files. Default: write
        to standard output

Careful reading of this suggests that:

• When the trimmed output is sent to a file with the -o output.fastq option,
  • diagnostics are written to standard output
    
    • so can be redirected to a log file with 1> small.trim.log
  • cutadapt -a CGTAATTCGCG -o small.trim.fq  small.fq 1> small.trim.log
• But when the -o option is omitted, and output goes to standard output,
  
  • diagnostics must be written to standard error
    • so can be redirected to a log file with 2> trim.log
  • cutadapt -a CGTAATTCGCG small.fq 1> small.trim.fq 2> small.trim.log
    

mkdir -p $SCRATCH/core_ngs/cutadapt
cd $SCRATCH/core_ngs/cutadapt
cp $CORENGS/human_stuff/Sample_H54_miRNA_L004_R1.cat.fastq.gz .
cp $CORENGS/human_stuff/Sample_H54_miRNA_L005_R1.cat.fastq.gz .
cp $CORENGS/custom_tracksalignment/Yeast_RNAseq_L002_R1.fastq.gz .
cp $CORENGS/custom_tracksalignment/Yeast_RNAseq_L002_R2.fastq.gz .

The BioITeam has an a number of useful NGS scripts that can be executed by anyone on ls6. or stampede2 stampede3. They are located in the /work/projects/BioITeam/common/script/ directory.

For groups that participate in BRCF pods, the scripts are available in /mnt/bioi/script on any compute server.

cd $SCRATCH/core_ngs/cutadapt
launcher_creator.py -j cuta.cmds -n cuta -t 01:00:00 -a OTH21164 -q normal 
sbatch --reservation=CoreNGS-Wed cuta.slurm
showq -u

# or, if you're not on the reservation:
launcher_creator.py -j cuta.cmds -n cuta -t 01:00:00 -a OTH21164 -q development
sbatch cuta.slurm
showq -u

echo "$((`zcat yeast_rnaseq_R1.cuta.fastq.gz | wc -l` / 4))"
zcat yeast_rnaseq_R2.cuta.fastq.gz | wc -l | awk '{printf("%d\n", $1/4)}'

For more on printf, which is available in most programming languages, see see https://en.wikipedia.org/wiki/Printf#Format_specifier or https://alvinalexander.com/programming/printf-format-cheat-sheet/