Tutorial:use the tool slicer to split big files (like FASTQ) to smaller files for parallel processing
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6.8 years ago
chen ★ 2.5k


Slice a text file to smaller files by lines, with gzip compression for input/output supported. This tool can be used to slice big FASTQ files to smaller ones for parallel processing. See https://github.com/OpenGene/slicer


# simplest
slicer -i <input_file_name> -l <how_many_lines_per_slice>

# specify a folder to store the sliced files
slicer -i <input_file_name> -l <how_many_lines_per_slice> -o <output_dir>

# force gzip
slicer -i <input_file_name> -l <how_many_lines_per_slice> -o <output_dir> --gzip


Assuming that you have a text file called filename.for.test.data with 400000 lines, you want to cut it to 4 slices (100000 lines for each). You'd like to gzip all the slices, keep the file extension .data, and store them in a folder sliced. You can use following command:

slicer -i filename.for.test.data -l 100000 -o sliced -e data -z -s

Then you will get four files in the folder sliced:


Get slicer

## Download
Get latest
# download by http

# or clone by git
git clone https://github.com/OpenGene/slicer.git

Get the stable releases


slicer only depends on libz, which is always available on Linux or Mac systems. If your system has no libz, install it first.

cd slicer


After build is done, run

sudo make install

Full options

usage: ./slicer --input=string --line=int [options] ... 
  -i, --input          input file name (string)
  -o, --outdir         the output folder, default is currently working directory (string [=.])
  -l, --line           how many lines per slice (int)
  -d, --digits         the digits for the slice number padding (1~10), default is 4, so the filename will be padded as 0001.xxx, 0 to disable padding (int [=4])
  -z, --gzip           force gzip output, default the gzip setting is following the input
  -n, --nogzip         don't use gzip output, default the gzip setting is following the input
  -c, --compression    the gzip compression level (0 ~ 9), 0 for best speed, 9 for best compression ratio, default is 2 (int [=2])
  -s, --simple_name    use the simple file name like 0001, and discard the original file name
  -e, --ext            set the file extension to be added to the output if using simple_name. This option only works when --simple_name enabled (string [=])
  -?, --help           print this message

Work with FASTQ

  • Make sure you set the line number (-l xxxx, or --line=xxxx) correctly as a multiple of 4, since each record always has 4 lines.
  • If you want to keep the .fq or .fastq file extension, you can set the extension by --ext=fq or --ext=fastq
  • If your data are paired-end sequencing files, you can run this tool for the pair of files separately.
  • If your data are paired-end sequencing files, and you enable the simple_name to use short file name. For read1, you can set the extension as R1.fq by --ext=R1.fq, and for read2 you can set R2.fq by --ext=R2.fq, then you will get the sliced files like 0001.R1.fq, 0002.R2.fq.
opengene slicer fastq splitter • 3.3k views

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