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XTRACT(1) NCBI Entrez Direct User's Manual XTRACT(1)


xtract - NCBI Entrez Direct XML conversion and transformation tool


xtract [-help] [-strict] [-mixed] [-self] [-accent] [-ascii] [-compress] [-stops] [-input filename] [-transform filename] [-aliases filename] [-pattern expr] [-group expr] [-block expr] [-subset expr] [-path path] [-if expr [constraint]] [-unless expr [constraint]] [-and condition] [-or condition] [-else] [-position pos] [-equals str] [-contains str] [-includes str] [-is-within str] [-starts-with str] [-ends-with str] [-is-not str] [-is-before str] [-is-after str] [-matches str] [-resembles str] [-is-equal-to expr] [-differs-from expr] [-gt N] [-ge N] [-lt N] [-le N] [-eq N] [-ne N] [-ret str] [-tab str] [-sep str] [-pfx str] [-sfx str] [-rst] [-clr] [-pfc str] [-deq str] [-def str] [-lbl str] [-set tag] [-rec tag] [-wrp tag] [-enc tag] [-plg str] [-elg str] [-pkg tag] [-fwd str] [-awd str] [-tag tag] [-att key value] [-cls] [-slf] [-end tag] [-element element] [-first element] [-last element] [-backward element] [-NAME] [--STATS] [-num element] [-len element] [-sum element] [-acc element] [-min element] [-max element] [-inc element] [-dec element] [-sub element] [-avg element] [-dev element] [-med element] [-mul element] [-div element] [-mod element] [-bin element] [-oct element] [-hex element] [-bit element] [-pad element] [-encode element] [-upper element] [-lower element] [-chain element] [-title element] [-mirror element] [-alnum element] [-basic element] [-plain element] [-simple element] [-author element] [-prose element] [-terms element] [-words element] [-pairs element] [-order element] [-reverse element] [-letters element] [-clauses element] [-year element] [-month element] [-date element] [-page element] [-auth element] [-initials element] [-jour element] [-trim element] [-wct element] [-doi element] [-translate element] [-classify element] [-replace -reg target -exp replacement] [-revcomp] [-nucleic] [-fasta] [-ncbi2na] [-ncbi4na] [-molwt] [-0-based element] [-1-based element] [-ucsc-based element] [-insd arg ...] [-histogram] [-e2index [extras]] [-indices element] [-article element] [-abstract element] [-paragraph element] [-stemmed element] [-head str] [-tail str] [-hd str] [-tl str] [-select condition] [-in filename] [-sort[-fwdelement] [-sort-rev element] [-format fmt [-unicode style]] [-verify] [-outline] [-synopsis] [-contour [delimiter]] [-examples] [-unix] [-version]


xtract converts an XML document into a table of data values according to user-specified rules.


Processing Flags

Remove HTML and MathML tags.
Allow mixed content XML.
Allow detection of empty self-closing tags.
Delete Unicode accents and diacritical marks.
Convert Unicode to numeric HTML character entities.
Compress runs of spaces.
Retain stop words in selected phrases.

Data Source

Read XML from file instead of standard input.
File of substitutions for -translate.
Mappings file for -classify operation.

Exploration Argument Hierarchy

Name of record within set. Use of different argument names allows command-line control of nested looping.

Path Navigation

Explore by list of adjacent object names.

Exploration Constructs


Conditional Execution

Element (or @attribute) must exist and satisfy any specified constraint.
Skip if element matches.
Preceding and following tests must both pass.
Any passing test suffices.
Execute if conditional test failed.

String Constraints

String must match exactly.
Substring must be present.
Substring must match at word boundaries.
String must be present.
Substring must be at beginning.
Substring must be at end.
String must not match.
First string < second string.
First string > second string.
Matches without commas or semicolons.
Requires all words, but in any order.

Object Constraints

Object values must match.
Object values must differ.

Numeric Constraints

Greater than.
Greater than or equal to.
Less than to.
Less than or equal to.
Equal to.
Not equal to.

Format Customization

Override line break between patterns.
Replace tab character between fields.
Separator between group members.
Prefix to print before group.
Suffix to print after group.
Reset -sep through -elg.
Clear queued tab separator.
Preface combines -clr and -pfx.
Delete and replace queued tab separator.
Default placeholder for missing fields.
Insert arbitrary text.

XML Generation

XML tag for entire set.
XML tag for each record.
Wrap elements in XML object.
Encase instance in XML object.
Prologue to print before instance.
Epilogue to print after instance.
Package subset in XML object.
Foreword to print before subset.
Afterword to print after subset.

Tag and Attribute Construction

Start with <tag.
Attribute key and value.
Close with >.
Self-close with />.
End contents with </tag>.

Element Selection

Print all items that match tag name.
Only print value of first item.
Only print value of last item.
Print values in reverse order.
Record value in named variable.
Accumulate values into variable.

-element Constructs

"Title[phospholipase | rattlesnake]"
Object Count

Special -element Operations

Object Name
Object Value

Numeric Processing

Bit count.
Zero-pad to eight digits.

Character Processing

XML-encode <, >, &, ", and ' characters.
Convert text to uppercase.
Convert text to lowercase.
Change spaces to underscores.
Capitalize initial letters of words.
Reverse order of letters.
Non-alphanumeric characters to space.

String Processing

Convert superscripts and subscripts.
Remove embedded mixed-content markup tags.
Normalize accented letters; spell Greek letters.
Multi-step author cleanup.
Text conversion to ASCII.

Text Processing

Partition text at spaces.
Split at punctuation marks.
Adjacent informative words.
Rearrange words in sorted order.
Reverse words in string.
Separate individual letters.
Break at phrase separators.

Citation Functions

Extract first 4-digit year from string.
Match first month name and return a corresponding integer.
YYYY/MM/DD from -unit "PubDate" -date "*"
Get digits (and letters) of first page number.
Change GenBank authors to Medline form.
Parse initials from forename or given name.
Clean up journal name punctuation.
Remove extra spaces and leading zeros.
Count number of -words in a string.
Add prefix, URL encode.

Value Transformation

Substitute values with -transform table.
Substring word or phrase matches to -aliases table.

Regular Expression

Substitute text using regular expressions.
Target expression.
Replacement pattern.

Sequence Processing

Reverse complement nucleotide sequence.
Subrange determines forward or revcomp.
Split sequence into blocks of 70 uppercase letters.
Expand ncbi2na to IUPAC. (May need to truncate result to actual sequence length.)
Expand ncbi4na to IUPAC. (May need to truncate result to actual sequence length.)
Calculate molecular weight of peptide.

Sequence Coordinates

-0-based element
-1-based element

Command Generator

Generate INSDSeq extraction commands. Print them if invoked standalone; run them if invoked as part of a pipeline. Requires one or more arguments, which may appear in the following order:
INSDSeq_sequence/INSDSeq_definition/INSDSeq_division/... [...]
INSDFeature_key/"#INSDInterval"/gene/product/feat_location/sub_sequence/... [...]

Frequency Table

Collects data for sort-uniq-count(1) on entire set of records.

Entrez Indexing

Create Entrez index XML. extras (true or false; false by default) indicates whether to index extra fields.
Index normalized words.
Title positional index.
Abstract positional index.
Index text paragraphs.
Apply Porter2 algorithm.

Output Organization

Print before everything else.
Print after everything else.
Print before each record.
Print after each record.

Record Selection

Select record subset by conditions.
File of identifiers to use for selection.

Record Rearrangement

Element to use as sort key.
Sort records in reverse order.


Fast block copy (still applies processing flags).
Compress runs of spaces.
Suppress line indentation.
Indent according to nesting depth.
Place each attribute on a separate line.


Report XML data integrity problems.


Display outline of XML structure.
Display individual XML paths.
Display XML paths to leaf nodes (delimited by / by default).

Full Exploration Command Precedence


Print usage information and some example argument combinations.
Complete usage examples, involving additional Entrez Direct tools.
Illustrate common Unix command arguments.
Print version number.


String constraints use case-insensitive comparisons.

Numeric constraints and selection arguments use integer values.

-num and -len selections are synonyms for Object Count (#) and Item Length (%).

-words, -pairs, and -indices convert to lower case.


archive-pmc(1), archive-pubmed(1), custom-index(1), disambiguate-nucleotides(1), download-ncbi-data(1), ds2pme(1), esample(1), fetch-pmc(1), fetch-pubmed(1), find-in-gene(1), fuse-segments(1), gene2range(1), hgvs2spdi(1), index-extras(1), index-pubmed(1), pma2pme(1), rchive(1), snp2hgvs(1), snp2tbl(1), sort-uniq-count(1), spdi2tbl(1), tbl2prod(1), transmute(1), uniq-table(1), xml2fsa(1), xml2tbl(1), xy-plot(1).

2023-03-31 NCBI