Linux Intro and NGS File Formats

NGS WTAC 2015

David Jackson

WTSI

Shell, Running Commands

Open a terminal to get a shell
Running commands
- ```
w
```
  gives machine load
- ```
ps
```
  or
```
ps x
```
  or
```
ps aux
```
  to see processes
Help for commands
- ```
man ps
```
  or just web search....
Different shells:
```
tcsh
```
,
```
bash
```
Leaving a shell:
```
exit
```
, ctrl-D

N.b. easy and quite universal remote access

Navigation and Manipulation of Directories

```
ls -lart
```
to see files in current directory. Nb "." and ".."
```
ls /usr/bin
```
or in another directory
```
ls /usr/bin/x*
```
or files matching a wildcard
```
pwd
```
to see current location

cd /usr/bin; pwd; cd; pwd; cd -; pwd; cd

move around hierarchy

mkdir -p super/dooper/results; ls -l super

creating a hierarchy

mv super/dooper super/duper; ls -l super

renaming a directory (or file)

```
rm -r super; ls -l super 
```
removing a hierarchy
Using a semi-colon allows you to perform a series of commands without having to wait for each one to complete

External Drives

Plug in your USB drive
```
df -T -h
```
can help you find where it is "mounted"
Change to that directory
Make and move into a directory
When finished, remember to move out of the directory (close shell or change directory) and then tell the OS to "safely remove" unmount the usb drive
Now move back to your home directory, then make and move into a directory for this tutorial

Fasta Sequence Data Files

and Text File Manipulation

```
wget ftp://ftp.sanger.ac.uk/pub/teams/117/WTAC/phix-illumina.fa
```
let's download a fasta sequence file for phiX (from the command line or just use your browser)
```
head -n 5 phix-illumina.fa
```
to inspect the first few lines
```
tail -n 5 phix-illumina.fa
```
to inspect the last few lines
```
wc phix-illumina.fa
```
to get the number of lines, words, and characters

Fasta Sequence Data Files

and Text File Manipulation

wget 'ftp://ftp.sanger.ac.uk/pub/teams/117/WTAC/adapters.fasta'

another fasta file with adapter sequence

```
cat adapters.fasta
```
spill the whole file to the terminal
```
less adapters.fasta
```
simple viewer for the terminal
```
grep -c -E '^>' adapters.fasta
```
count the number of sequence records
```
grep -A 2 RNA adapters.fasta
```
show (first line of) RNA related records

Fastq Sequence Data Files

and Using the Shell

```
echo foo{1,3,5}{A,B} okay
```
prints the shell expanded strings

wget ftp://ftp.sanger.ac.uk/pub/teams/117/WTAC/s6823_1_{1,2,t}_phix.fastq

download 3 fastq sequence files with phiX reads

```
head -n 6 s6823_1_{1,2,t}_phix.fastq
```
to inspect the first few lines of each file
```
wc s6823_1_*_phix.fastq
```
to get the number of lines, words, and characters
How many sequence records?
Phred qualities: -10*log_10(P_error) beware of different encodings

Pipes and Data Redirection

md5sum s6823_1_1_phix.fastq > s6823_1_1_phix.fastq.md5

output of the md5sum program is put in a file

```
cat s6823_1_1_phix.fastq.md5
```
```
for f in *.fastq; do md5sum $f > $f.md5; done
```
loop through all the fastq files creating corresponding md5 files
```
cat s6823_1_{1,2,t}_phix.fastq | wc
```
output of a process can also be redirected to another process
```
tar cf - s6823_1_{1,2,t}_phix.fastq | gzip -9 > s6823_1_phix.tgz
```
uses a pipe and a redirect to create a compressed archive of the fastq files (reduced IO)
```
gunzip -c s6823_1_phix.tgz | tar tf -
```
lists the contents of the archive

Process Control

```
xeyes
```
then ctrl-C to terminate it
```
xeyes
```
then
- ctrl-Z to suspend the process
- ```
bg
```
  to allow it to continue running in the background
```
xeyes &
```
to start a process running in the background
```
jobs
```
to see background processes, jobs, of this shell
```
ps
```
shows processes of this session
```
kill %1
```
to terminate the first xeyes
```
kill
```
2nd xeyes PID for the second
```
top
```
for a full terminal updating display of processes running on the system

SAM (& BAM) Sequence & Alignment Files

http://www.htslib.org/ for the specification and links
Samtools and Picard are the leading tools
Biobambam also used also at WTSI
Text (e.g. .sam files) and binary (e.g. .bam files) formats

wget ftp://ftp.sanger.ac.uk/pub/teams/117/WTAC/s6823_1_phix.sam

```
head s6823_1_phix.sam
```
header records start with @, tab delimited fields identified by two character tags followed by a :
```
grep -v -E '^@' s6823_1_phix.sam | head
```
separate sequence/alignment data records for paired reads (subreads), tab delimited fields (11 mandatory folowed by optional tag identified fields)

Samtools

obtaining and building

wget https://github.com/samtools/samtools/releases/download/1.2/samtools-1.2.tar.bz2 \
 && tar xjf samtools-1.2.tar.bz2

download and if download is successful uncompress some samtools source

```
cd samtools-1.2; ls;  make -j 2
```
```
ls; cd .. 
```
```
samtools-1.2/samtools
```
```
samtools-1.2/samtools help view
```
```
man samtools-1.2/samtools.1 
```

Samtools

using

samtools-1.2/samtools view -bS s6823_1_phix.sam  > s6823_1_phix.bam

convert SAM to BAM

```
file s6823_1_phix.bam s6823_1_phix.sam
```
not normally interesting to look directly in binary files....
```
ls -lh s6823_1* 
```
compare the sizes of the files....
```
samtools-1.2/samtools flagstat s6823_1_phix.bam
```
for some useful stats (dependant on how it's been created)
```
samtools-1.2/samtools index s6823_1_phix.bam 
```
creating an index allows fast reference location access

samtools-1.2/samtools tview s6823_1_phix.bam phix-illumina.fa

reference based text viewer -- boring for phiX

Samtools & CRAM

New format to try to help with growing data volumes
Lossy and lossless modes

samtools-1.2/samtools view -T phix-illumina.fa -CS s6823_1_phix.sam  > s6823_1_phix.cram

convert SAM to CRAM

```
ls -lh s6823_1* 
```
compare the sizes of the files....

samtools-1.2/samtools view -h s6823_1_phix.cram | less

to convert to SAM and pipe to a "pager" (q to quit)

CRAM functionality in samtools approaching that of BAM....

Illumina Runfolder Anatomy

Structure

```
InterOp
```
```
Data/Intensities
```
```
Data/Intensities/BaseCalls
```

Data file types: (c)locs, filter, control, bcl, cif

So...

Sequence file formats
- fasta, fastq, sam/bam : you're most likely to work with today
- cram : smaller than bam, v2.1 now, next likely common format
- sff, srf, sra, ztr : there are plenty of other formats which typically contain more "raw" data
- Illumina: (c)locs, filter, control, bcl → fastq
Using the shell
- is a "universal" language
- gives you a
```
history
```
- can get the computer to do the (boring) repetative stuff completely consistently
- allows you wrap an established procedure in to a script....

Questions?

Samtools & flagstat, stats/bamcheck

samtools-1.2/samtools view -u \
ftp://ngs.sanger.ac.uk/scratch/project/WTAC/processed_data/12585_1#21.bam \
| samtools-1.2/stats - | tee 12585_1#21.bam.bamstats

pull your data from ftp site, push it uncompressed through bamcheck, and both write bamcheck's output to the terminal and to a file

samtools/misc/plot-bamstats -p 12585_1#21/ 12585_1#21.bam.bamstats

create some plots using the bamcheck data

Picard

Download and uncompress/install Picard
Try converting from BAM to fastq

FastQC

From Babraham Institute - neighbours up the road...
Download and uncompress/install FastQC
Try inspecting BAM or fastq files

samtools & pileup

samtools-1.2/samtools faidx phix-illumina.fa

create an index for reference fasta file

```
cat phix-illumina.fa.fai 
```
it's quite boring for this reference

samtools-1.2/samtools mpileup -f phix-illumina.fa s6823_1_phix.bam | less -S

IGV

Inspect your BAM file with IGV

Biobambam

Download and uncompress/install Biobambam
Try marking duplicates using Biobambam and compare with Picard

WTSI -- 15/04/2015

NGS WTAC 2015 -- Linux Intro and NGS File Formats

Linux Intro and NGS File Formats

NGS WTAC 2015

David Jackson

WTSI

Shell, Running Commands

Navigation and Manipulation of Directories

External Drives

Fasta Sequence Data Files

and Text File Manipulation

Fasta Sequence Data Files

and Text File Manipulation

Fastq Sequence Data Files

and Using the Shell

Pipes and Data Redirection

Process Control

SAM (& BAM) Sequence & Alignment Files

Samtools

obtaining and building

Samtools

using

Samtools & CRAM

Illumina Runfolder Anatomy

So...

Samtools & flagstat, stats/bamcheck

Picard

FastQC

samtools & pileup

IGV

Biobambam