Ubuntu Manpage: samtools-view - views and converts SAM/BAM/CRAM files

NAME

       samtools-view - views and converts SAM/BAM/CRAM files

SYNOPSIS

       samtools view [options] in.sam|in.bam|in.cram [region...]

DESCRIPTION

       With  no  options  or  regions specified, prints all alignments in the specified input alignment file (in
       SAM, BAM, or CRAM format) to standard output in SAM format (with no header).

       You may specify one or more space-separated region specifications after the input  filename  to  restrict
       output  to  only  those  alignments  which  overlap the specified region(s). Use of region specifications
       requires a coordinate-sorted and indexed input file (in BAM or CRAM format).

       The -b, -C, -1, -u, -h, -H, and -c options change the output format from the default of  headerless  SAM,
       and the -o and -U options set the output file name(s).

       The  -t  and  -T options provide additional reference data. One of these two options is required when SAM
       input does not contain @SQ headers, and the -T option is required whenever writing CRAM output.

       The -L, -M, -N, -r, -R, -d, -D, -s, -q, -l, -m, -f, -F, and -G options filter the alignments that will be
       included in the output to only those alignments that match certain criteria.

       The -x, -B, --add-flags, and --remove-flags options modify the data which is contained in each alignment.

       The -X option can be used to allow user to specify customized index file location(s) if the  data  folder
       does not contain any index file. See EXAMPLES section for sample of usage.

       Finally,  the -@ option can be used to allocate additional threads to be used for compression, and the -?
       option requests a long help message.

       REGIONS:
              Regions can be specified as: RNAME[:STARTPOS[-ENDPOS]] and all position coordinates are 1-based.

              Important note: when multiple regions are given, some alignments may be output multiple  times  if
              they overlap more than one of the specified regions.

              Examples of region specifications:

              chr1      Output all alignments mapped to the reference sequence named `chr1' (i.e. @SQ SN:chr1).

              chr2:1000000
                        The  region  on  chr2  beginning at base position 1,000,000 and ending at the end of the
                        chromosome.

              chr3:1000-2000
                        The 1001bp region on chr3 beginning at base position 1,000 and ending at  base  position
                        2,000 (including both end positions).

              '*'       Output  the  unmapped reads at the end of the file.  (This does not include any unmapped
                        reads placed on a reference sequence alongside their mapped mates.)

              .         Output all alignments.  (Mostly unnecessary as not specifying a region at  all  has  the
                        same effect.)

OPTIONS

-b, --bam Output in the BAM format.

-C, --cram
Output in the CRAM format (requires -T).

-1, --fast
Enable fast BAM compression (implies -b).

-u, --uncompressed
Output uncompressed BAM. This option saves time spent on compression/decompression and is thus
preferred when the output is piped to another samtools command.

-h, --with-header
Include the header in the output.

-H, --header-only
Output the header only.

--no-header
When producing SAM format, output alignment records but not headers. This is the default; the
option can be used to reset the effect of -h/-H.

-c, --count
Instead of printing the alignments, only count them and print the total number. All filter
options, such as -f, -F, and -q, are taken into account.

-?, --help
Output long help and exit immediately.

-o FILE, --output FILE
Output to FILE [stdout].

-U FILE, --unoutput FILE, --output-unselected FILE
Write alignments that are not selected by the various filter options to FILE. When this option
is used, all alignments (or all alignments intersecting the regions specified) are written to
either the output file or this file, but never both.

-t FILE, --fai-reference FILE
A tab-delimited FILE. Each line must contain the reference name in the first column and the
length of the reference in the second column, with one line for each distinct reference. Any
additional fields beyond the second column are ignored. This file also defines the order of the
reference sequences in sorting. If you run: `samtools faidx <ref.fa>', the resulting index file
<ref.fa>.fai can be used as this FILE.

-T FILE, --reference FILE
A FASTA format reference FILE, optionally compressed by bgzip and ideally indexed by samtools
faidx. If an index is not present one will be generated for you, if the reference file is
local.

If the reference file is not local, but is accessed instead via an https://, s3:// or other
URL, the index file will need to be supplied by the server alongside the reference. It is
possible to have the reference and index files in different locations by supplying both to this
option separated by the string "##idx##", for example:

-T ftp://x.com/ref.fa##idx##ftp://y.com/index.fa.fai

However, note that only the location of the reference will be stored in the output file header.
If this method is used to make CRAM files, the cram reader may not be able to find the index,
and may not be able to decode the file unless it can get the references it needs using a
different method.

-L FILE, --target-file FILE, --targets-file FILE
Only output alignments overlapping the input BED FILE [null].

-M, --use-index
Use the multi-region iterator on the union of a BED file and command-line region arguments.
This avoids re-reading the same regions of files so can sometimes be much faster. Note this
also removes duplicate sequences. Without this a sequence that overlaps multiple regions
specified on the command line will be reported multiple times. The usage of a BED file is
optional and its path has to be preceded by -L option.

--region-file FILE, --regions-file FILE
Use an index and multi-region iterator to only output alignments overlapping the input BED
FILE. Equivalent to -M -L FILE or --use-index --target-file FILE.

-N FILE, --qname-file FILE
Output only alignments with read names listed in FILE.

-r STR, --read-group STR
Output alignments in read group STR [null]. Note that records with no RG tag will also be
output when using this option. This behaviour may change in a future release.

-R FILE, --read-group-file FILE
Output alignments in read groups listed in FILE [null]. Note that records with no RG tag will
also be output when using this option. This behaviour may change in a future release.

-d STR1[:STR2], --tag STR1[:STR2]
Only output alignments with tag STR1 and associated value STR2, which can be a string or an
integer [null]. The value can be omitted, in which case only the tag is considered.

-D STR:FILE, --tag-file STR:FILE
Only output alignments with tag STR and associated values listed in FILE [null].

-q INT, --min-MQ INT
Skip alignments with MAPQ smaller than INT [0].

-l STR, --library STR
Only output alignments in library STR [null].

-m INT, --min-qlen INT
Only output alignments with number of CIGAR bases consuming query sequence ≥ INT [0]

-e STR, --expr STR
Only include alignments that match the filter expression STR. The syntax for these expressions
is described in the main samtools(1) man page under the FILTER EXPRESSIONS heading.

-f FLAG, --require-flags FLAG
Only output alignments with all bits set in FLAG present in the FLAG field. FLAG can be
specified in hex by beginning with `0x' (i.e. /^0x[0-9A-F]+/), in octal by beginning with `0'
(i.e. /^0[0-7]+/), as a decimal number not beginning with '0' or as a comma-separated list of
flag names.

For a list of flag names see samtools-flags(1).

-F FLAG, --excl-flags FLAG, --exclude-flags FLAG
Do not output alignments with any bits set in FLAG present in the FLAG field. FLAG can be
specified in hex by beginning with `0x' (i.e. /^0x[0-9A-F]+/), in octal by beginning with `0'
(i.e. /^0[0-7]+/), as a decimal number not beginning with '0' or as a comma-separated list of
flag names.

-G FLAG Do not output alignments with all bits set in INT present in the FLAG field. This is the
opposite of -f such that -f12 -G12 is the same as no filtering at all. FLAG can be specified
in hex by beginning with `0x' (i.e. /^0x[0-9A-F]+/), in octal by beginning with `0' (i.e.
/^0[0-7]+/), as a decimal number not beginning with '0' or as a comma-separated list of flag
names.

-x STR, --remove-tag STR
Read tag to exclude from output (repeatable) [null]

-B, --remove-B
Collapse the backward CIGAR operation.

--add-flags FLAG
Adds flag(s) to read. FLAG can be specified in hex by beginning with `0x' (i.e. /^0x[0-9A-
F]+/), in octal by beginning with `0' (i.e. /^0[0-7]+/), as a decimal number not beginning with
'0' or as a comma-separated list of flag names.

--remove-flags FLAG
Remove flag(s) from read. FLAG is specified in the same way as with the --add-flags option.

--subsample FLOAT
Output only a proportion of the input alignments, as specified by 0.0 ≤ FLOAT ≤ 1.0, which
gives the fraction of templates/pairs to be kept. This subsampling acts in the same way on all
of the alignment records in the same template or read pair, so it never keeps a read but not
its mate.

--subsample-seed INT
Subsampling seed used to influence which subset of reads is kept. When subsampling data that
has previously been subsampled, be sure to use a different seed value from those used
previously; otherwise more reads will be retained than expected. [0]

-s FLOAT Subsampling shorthand option: -s INT.FRAC is equivalent to --subsample-seed INT --subsample
0.FRAC.

-@ INT, --threads INT
Number of BAM compression threads to use in addition to main thread [0].

-S Ignored for compatibility with previous samtools versions. Previously this option was required
if input was in SAM format, but now the correct format is automatically detected by examining
the first few characters of input.

-X, --customized-index
Include customized index file as a part of arguments. See EXAMPLES section for sample of usage.

--no-PG Do not add a @PG line to the header of the output file.

EXAMPLES

o Import SAM to BAM when @SQ lines are present in the header:

samtools view -bo aln.bam aln.sam

If @SQ lines are absent:

samtools faidx ref.fa
samtools view -bt ref.fa.fai -o aln.bam aln.sam

where ref.fa.fai is generated automatically by the faidx command.

o Convert a BAM file to a CRAM file using a local reference sequence.

samtools view -C -T ref.fa -o aln.cram aln.bam

o Convert a BAM file to a CRAM with NM and MD tags stored verbatim rather than calculating on the fly
during CRAM decode, so that mixed data sets with MD/NM only on some records, or NM calculated using
different definitions of mismatch, can be decoded without change. The second command demonstrates how
to decode such a file. The request to not decode MD here is turning off auto-generation of both MD and
NM; it will still emit the MD/NM tags on records that had these stored verbatim.

samtools view -C --output-fmt-option store_md=1 --output-fmt-option store_nm=1 -o aln.cram aln.bam
samtools view --input-fmt-option decode_md=0 -o aln.new.bam aln.cram

o An alternative way of achieving the above is listing multiple options after the --output-fmt or -O
option. The commands below are equivalent to the two above.

samtools view -O cram,store_md=1,store_nm=1 -o aln.cram aln.bam
samtools view --input-fmt cram,decode_md=0 -o aln.new.bam aln.cram

o Include customized index file as a part of arguments.

samtools view [options] -X /data_folder/data.bam /index_folder/data.bai chrM:1-10

o Output alignments in read group grp2 (records with no RG tag will also be in the output).

samtools view -r grp2 -o /data_folder/data.rg2.bam /data_folder/data.bam

o Only keep reads with tag BC and were the barcode matches the barcodes listed in the barcode file.

samtools view -D BC:barcodes.txt -o /data_folder/data.barcodes.bam /data_folder/data.bam

o Only keep reads with tag RG and read group grp2. This does almost the same than -r grp2 but will not
keep records without the RG tag.

samtools view -d RG:grp2 -o /data_folder/data.rg2_only.bam /data_folder/data.bam

o Remove the actions of samtools markdup. Clear the duplicate flag and remove the dt tag, keep the
header.

samtools view -h --remove-flags DUP -x dt -o /data_folder/dat.no_dup_markings.bam /data_folder/data.bam

AUTHOR